How can I add a series parallel switch to my J-bass?

I would like to add a little custom wiring to my bass, that would allow me to replace one of my volume pots with a push/pull type pot, that I could use as a series parallel switch, a la the Fender S-1 Switching system. I know how to add a basic series parallel switch, but how can I do this, whilst still having a seperate volume control for each pickup?

Just replace the P pickup in the diagram with a J.
Oh, the phase stays the same too.

I know how to add a basic series parallel switch, but how can I you can't have separate volume controls if the pups are in series.