Nah don't bother adding the resister unless you really want to. I'd just fit a 500k linear pot opposite the vol pot so the lugs are mirrored. Then wire a cap (my fav is 0.022uF) between the centre lug of the tone pot and the left lug of the vol pot. Then solder the left lug of the tone pot to its base.
Thanks! I think I get it now. I was over-complicating the DPDT switch in my mind. Baylin's post helped me to mentally separate the switch portion from the pot portion of the push/pull pot. Makes sense now, I was way overthinking it.
Thanks to both of you for advice on the resistor. I'll just leave it as a 500K for the single coil.