Attn: Tim ...

[Kent S.]

Here's what you want, it's real simple, just add the jumper wire shown in blue. I have no way of knowing the phase relationship of the existing pups, so just following the directions if the middle and neck pup are out of phase.
Thanks to SD for allowing me to butcher their artwork ...
Everything you need to know is shown on there, most of everything you won't even have to touch.