The AE1P has no actual built in multiple exposure facility. You would have to move up to the A1 for that - a camera that is very much like an "advanced" AE1P (I believe the body is actually largely the same as would be suggested by the interchangeable motor drives, "sprots" grips, etc).
You can fool the camera, though, by pressing the film rewind button and cocking the shutter - but I can't guarantee how precisely the film will remainin place. Theoretically, the shutter will cock, but the film transport, being disengaged, won't move the film.
It may be worth a shot - or you may want to get an A1 - they are really quite a bargain given what you pay vs what you get. Some other FD mount cameras that have multiple exposure facilities are the EF, all the F1's (new, New and the original), the already mentioned A1, and the T90 (I think). I can't think of any others, but you would be unlikely to be unhappy with any of the above.
Peter.