Here are a set of wiring diagrams that make nifty use of a resistor when combining humbuckers with single coils in Telecaster wiring setups. Both diagrams use 500k volume and tone pots. Soldering a 470k resistor from the single coil pickup connection on the switch to ground means that when the single coil is selected, it actually sees approximately 250k volume pot resistance instead of 500k.
Try this setup for yourself using our HS Telecaster wiring kit.
If you want to play around with resistor values, use a parallel resistance calculator, putting the value of your potentiometer as one of the resistors.