My Sport had a bit of a dent (from the previous owner leaving it on the cart), but I found that leaving it off the cart (on the side, whatever) helped lessen the dent. Also, a bit of heat - in my case a 43 degree day - helped it to 'pop' out a bit more.
I guess you could also apply some external heat and some internal pressure to assist, but I''d be careful. Since polyethylene is a thermoplastic, it can be 'remoulded' to a certain extent, but too much heat and you can do serious damage! Once the dent is out, rapid cooling of the plastic (pour some ice-water on it) will help it to 'set' in the new position...
If in doubt, talk to a Hobie dealer, I guess they deal with this issue a lot...
PB (roadkills): fox 85cm, rabbit 32cm, dove 26cm, dragonfly 11cm, mega-moth 9cm, hippy 195cm