I've planned to do either one of these.
This you don't need to buy anything extra
If anyone wants to try this wiring on a Squier VI, note that you will have to disconnect the small wire that goes from the ground (black) wire to the metal pickup claw on each of the 3 pickups.
Otherwise in series mode bridge and neck pickup are shorted.
(took me hours of fumbling and cursing until I finally figured that one out ...)
The claws will still be grounded through the mounting springs that contact the conductive paint covering the pickup cavities, so no worries
The series modes are super beefy!