Bristles as mentioned above love filters. They like to feel enclosed and mine even nested and reared a couple of broods in the top of one of mine. But it was a standard internal filter and he was in the bit at the top that can be removed to add on hoses so no moving parts thank goodness. I think the likley hood is he wont come out unless hes very hungry and the likleyhood of you being around to get the top back on is minimal. Cant you get your hands on a cheap internal filter that you can transfere media into until you can get him out. Its cheaper than going the external route, and means you have a spare if the other break or you have a similar problem.
Hope you get him out OK