I've already googled this a lot, but wasn't able to find a program or plugin to help me. I know about different methods for collision checking, so I wasn't looking for alternative methods, as the one I've decided on is best suited for my game. Anyway, I did a quick test and discovered that the boxes don't have to be all that precise - the effect is actually best if the boxes don't follow the edges of the image 100%, as this gives the effect of the object being 3D, since all bullets won't impact right on the edge but sometimes further in. It works perfectly. Almost seems to be pixel perfect collision, but a lot faster and not as clinically precise on the edges as pixel perfect collision would be. So, doing the boxes manually won't be quite as big a chore, since they don't need to be all that perfect.

(I'm using SDL and OpenGL, by the way.)