I'll wait.
...I know, right? I bet you're squirming with indignance, even if you've never worked as a server before, and/or you're concerned about the non-complimentary angle from which this piece serves up the Christian faith. Mmm, self-righteous deception for the glory of God. Delicious.
So let me begin (is it too late now to begin?) by saying that I think there's more to this than a critical view of Christianity. Some of Jesus' most controversial points were his criticisms of hypocrites and those who considered themselves most righteous. Today, this doesn't mean that we need to avoid Christianity or gathering as a faith community, but we do need to keep reimagining what it means to be a Christian while searching the core of Jesus' movement.
The article points out that not all Christians are
Instead of presuming to answer questions like these (since I think these are the sorts of questions best answered via actions), I'm going to highlight further what I consider a few important issues in the described scenario.
THE ISSUE OF DECEPTION

If their message is that there are things in life more important than money, are they making that point by getting a hard worker's hopes up, thinking they've received a good tip, just to fool them?
Why not just leave a message on a card or paper instead; why go through the trouble of using fake money? Which brings us to...
THE REAL, HUMAN CONCERNS OF THE STAFF
As written in James, faith without good works is dead, and it does little good to give someone spiritual guidance if their basic needs are ignored (very Maslow's Hierarchy of Needs, about 1800 years in advance).
By this example, should we replace all salaries with advice instead? How do the people leaving these tips support themselves? (And let's not pretend that a waiter's tip is beyond comparison to a wage, particularly if the employee's official salary is otherwise below legal minimum wage.)
Money is not the root of all evil; it has potential to do good, and technically it's just a tool in the extended bartering system of one person's time and labor in exchange for another's. So let's make every effort to make a fair trade.
THE GRATITUDE FACTOR
Traditionally, the amount of a tip is considered to be commensurate with the customer's gratitude and/or a measure of the quality of the service. Wait staff are often paid below minimum wage and depend greatly on their tips; unless stated, it's not included in the bill and the customer chooses the amount. A lack of tip signals extraordinarily bad service and/or extraordinarily ungrateful customers.
If a religious person is inclined to use this occasion to share the Gospel (more on that in a sec), they could do so separately and leave a note with the tip. Might look too much like bribing someone to convert, but tipping is being kind, generous, mindful of the server, and a decent customer. The note is just an additional and probably unsolicited expression of spiritual concern, whatever one's views on that matter. And speaking of which...
EVANGELISM IN ITSELF IS NOT A BAD THING
Mainstream Protestant churches and nonreligious groups sometimes villainize evangelism or proselytism, or else don't know what to do with it and shy away, but passive-aggressive practices like fake-tipping only fuel that fire.
At its best, (Christian) evangelism means sharing the Gospel, the good news - that something amazing has happened in Christ and continues to happen when the Spirit is at work in us. It means believing something so deeply that it simply must be shared; to avoid sharing altogether would imply that there's nothing so great or urgent there in the first place.
But the core of Christianity isn't about dropping a spiritual nugget of wisdom and running. Jesus and biblical writers like Paul emphasize community, unconditional love, and nurturing one another. Actually, these concepts being made reality are all a huge part of the message!
So telling others about Jesus isn't a bad thing, and these customers may genuinely believe that they're appropriately sharing an important message, but they've made no attempt to connect to the person in a truly meaningful way - nothing that demands risk or even much time and energy on their part. Unless they're chatty regulars, they're not around to nurture the server in faith or in general.
(Oh yeah. Sidenote: Casting Crowns touched on the idea of true Christian outreach and active care in the song "If We Are the Body.")

Mainly, it's my hope that the religious and non-religious folks who read and reflect on the aforementioned Daily Finance article walk away with something other than a bitterness for Christians and others who seem too "pushy" in sharing faith (as, I admit, I have been prone to feel).
I hope that there is something fortifying and renewing to be found here - perhaps faith-affirming, or at least reconciling.
One of my favorite things about taking Church History classes in seminary (besides inordinate gobs of song parody fodder) has been confronting some of the terrible things that Christians have done, often in God's name.
Being honest about this troubling history - and realizing that "my" church and I are not necessarily much holier - has opened me up to thinking about all the good potential the church still holds and, perhaps most inspirationally, how we as a faith community can grow beyond and despite our mistakes.