Got all the achievements, don't really have any hints on the posing, though the clown shoes should help with that, seemed more like luck to me.
for the 9 and 11 somersaults, hold down while spinning and you spin faster. Took me forever to figure that out, and they were my last two achievements, but i finally got them. For the 11, you could try hitting up just once at the beginning, then keep jumping and posing to build up your boost to full, then go and get a full jump and hold down with your spins
 "Flying Castle"){kind=icon}
 "Hanna in a Choppa 2"){kind=icon}
 "Ski Maniacs"){kind=icon}