Yeah, unfortunately it's very hard to provide praise, or technical challenges, with vesting:
"Great job! Is what I'll tell you about the project you just finished. But only if you're still here in two years!"
The nice thing about money is that it's so easy to fiddle around with it to get the incentives right. But I agree -- this doesn't work if the person you're dealing with isn't strongly motivated by money.
But the principle may hold true regardless of the method of rewarding.