It's not quite that easy - the DMR is both a back and a winder contoured to the R body shape. It requires some signaling between the camera and the back to synchronize the exposure -- you want to reset the sensor just before the shutter fires and read out just after, otherwise you get a lot more noise. Since the AE1P lacks that signalling, it would have to be hacked in. The back also bulges out a lot more than the Canon back which would make the AE1P viewfinder a PITA to use. If you mainly want to use Canon FD lenses, there are much better solutions.
Originally Posted by Diapositivo