I can't say I've used 3068 yet. However, assuming it's much like any other hefeweizen yeast, I'd ferment at 70 F, and that way you'll get your banana. And with an underpitch, maybe even more. For a serious underpitch, I'd use 1/4 the mrmalty.com recommended amount. So when he says you need like 2.5 liters for 5 gallons, screw it and just pitch a fully (or even just half?) swollen smackpack without any starter and it should turn out to your liking.
So far I'm a believer in underpitching as a viable means of awesomeness in hefs and Belgians. However, my experiments are yet to be run this summer in this regard. I'm sure I'll be surprised by something along the way. So, proceed, with caution.