I'm no whizz-kid when it comes to pedals or gear, but I read on some forum that it's done with a 2 pedal red boss delay/looper in combination with a stage mixer (don't ask me how). Another guess would be that he does it with an Akai Deep Impact SB1 or some sort of standalone sampling foot-pedal with variable-length sampling.
We'll probably never know. Happy hunting.
