There was a video on Discovery a few years back about this very thing, not sure if it was seat belt or something esle but the pilot could not cut the diver away and had to return with him hanging from the right main. It wasn't as bad as it sounded, because other than getting dragged on grass at 50 mph for a few hundreds yards the jumper was fine. I worry more about jumpers destroying the tail as they jump out than hanging from a main.

Too bad about the website.

Here's a little advice for jump pilots in situations like this. If you have to bring a diver back for any reason, in or out of the plane, always use a gentle descent rate (~500 fpm). They have a pyrotechnic deployment device as a backup for the main that has a pretty sensitive descent gauge calibrated to assume the diver has lost the main (or passed out) if the altitude is less than about 1500 agl and the descent rate is more than about 700 fpm.