There is this, I haven't watched it, but Steve White is very respected in reward training, he's something of a pioneer.
http://www.clickertraining.com/store/?item=trwistwhHe does this thing called scent in a bottle - if you google it you should find plenty of articles about it - which allows you to see that the dog is on the scent. I think that's a really smart idea.
I found this also, which is a Basenji doing it - not sure whether White's method is followed exactly, as I don't know the details of how he does it. (This owner makes the weirdest noises I've ever heard a trainer make - it's worth it just for that lol). At this stage, when the dog is going from treat to treat the scent line being visible to the owner (because it's wet) probably doesn't make that much difference to the older method of putting treats into where you stepped (although that might be more difficult when on a hard surface), but as the treats get spread out further or start to come from the hand, it will becomes more useful.
http://www.youtube.com/watch?v=d5MKvm6kl7wIf you can start on a hard surface, that's better, because then you don't later have to teach the dog to not follow the surface disturbance odours (which is what dogs trained on grass usually start out thinking they ought to follow), but to follow the human scent.