Hello. Welcome to the forum.
Depends on the type of switch. If you mean an LP-style switch, it won't work. If you mean a simple DPDT on-off-on switch, then its fairly simple. And, mind you, that will be a different switch from the pickup selector switch.
Thats not that difficult either. Unusual, but not difficult. I've got a couple of things in the works right now to switch in an L-pad in either of the split or parallel modes, so the output matches the series mode. Its not quite ready for prime time yet, but I'm close.
Stay tuna-ed.
Artie