I've had great results using a pitchshifter (1 octave up) and a tremelo effect for that whack-whack-whack sound. Using those effects I've programmed a good Lemon sound in my GX-700.
During the verses he is using the Slicer Delay Gate effect. He is playing during the pre chorus with a echo delay, chorus, and delay. And during the chorus he is playing, but it is really, really low in the mix.
When you say he's using the slicer, where is it located? Is it a rack effect? is it where his controlling system and whammy effect is? or is it on top of the racks?