Personally, I would avoid any effort to avoid putting on fat. No cardio, no thermogenics. If you notice that you're getting really fat really quick, just drop calories a bit until you're only gaining 1-2 lbs a week. That's a pretty safe protocol. Of course you could just go all out, and gain 5-8 lbs a week, but that would definitely put on some extra fat, assuming you're already in decent shape.