This is just off the top of my head, but I think it'll work as advertised:
Depending on the configuration of the balance pot (they can vary), from the centre detent turning it clockwise will keep the neck at 100% and decrease the bridge volume, turning it counter-clockwise will keep the bridge at 100% and decrease the neck volume. Swap the red/green pairs between the upper and lower lugs if you want to reverse the direction (red top, green bottom).
The coloured wiring is to show what needs to connect to where, but how you make those connections will ultimately depend on your layout. For instance, the ground wire (black) to the switch could be the shield on a two core cable (for the red and green) from the balance pot which then links to the pot's ground which goes to the common ground point on the tone pot etc. The No-Load tone pot is just a idea, a standard tone pot would be fine.