So, this thread:http://nerfhaven.com/forums/topic/27208-pump-action-reaper-writeup/
is for a different blaster, but you can do this mod even better with the retaliator, because the 1 1/4 inch pipe fits like a barrel extension on the retaliator muzzle.
So you stick about four inches of that on the muzzle,
then wrap some tape around the end of a one foot (approximately) long piece of one inch pvc, and shove it in the 1 1/4 inch piece on the muzzle.
Then, you put on the pump handle, and connect to the slide with a scrap bit of junk lying on the shop floor.
And then you have a ugly, but really practical pump. Am I making sense? If not, ask whatever questions you like. Related to the pump, of course.