I know I saw a thread around here a few years back about someone fermenting inside a pumpkin. From what I recall, it didn't go over well, I believe it got infected due to the difficulty of trying to sanitize a pumpkin.
At 1 week in (when it was served) it was good. Put a tap in the side of the pumpkin even. A bit funky, a bit sour (lambic maybe). Probably wouldn't have made it much past the week - but it was, IMHO, damn good.
For the two it won't works, I've also read a couple write-ups where it worked quite well. Start with a fresh firm pumpkin. Ferment cool or use a lager yeast in a refrigerator. Immediately crash cool for aging. Rack to second pumpkin quckly.