you might like to try this:
Altering Pickup Characteristics
Change the external load. This method is inexpensive but can be very effective. With only a little expense for electronic components, the sound can be shaped within wide limits. Standard tone controls lower the resonant frequency by connecting a capacitor in parallel with the pickup (usually through a variable resistor to give some control over how much the capacitor affects the pickup). Therefore, one way to change the sound is to replace the standard tone control potentiometer with a rotary switch that connects different capacitors across the pickup (a recommended range is 470 pF to 10 nF). This will give you much more sound variation than a standard tone control (Fig. 8).
yup that would be the same thing, only far more expensive than doing it yourself.
The original tone circuit based on capacitance I'm pretty sure was the Gibson varitone switch.
SO basically get a rotary switch that can handle 6 capacitors, put it where a tone pot used to be, connect the common tabs on the rotary across the positive and ground.