...really?
I was gonna suggest mda Roundpan for the lazy way to go about it. More technical approach would be to right click the pan knob for the VST (or mixer channel if you have it routed to one), hit edit event, when the new window pops up go to the top left of it (the arrow button), scroll to tools, and click LFO. You can then go as crazy or as basic as you want and set it to go in sync with your tempo.