Below is a diagram for HSH Strat using a 4 pole Oak Grigsby Super switch. The setup uses 500k pots and 0.022uF capacitors.
Below is a very simple setup that makes use of a single resistor running from the single coil connection on the switch to ground. By using 3 x 500k pots in this circuit, your neck and bridge humbuckers are seeing the correct value. When selecting the single coil position, the 470k resistor ensures the pickup reads 250k and not 500k. Simply solder the resistor from the switch to the back of the nearest pot.