If you have gauges with one + for main power, one + for illumination power, and one - for both power wires, how would you go about wiring them into the stock dimmer?

The stock dimmer varies voltage on a ground side of the circuit, not the power side. Therefor, if I wired the dimmers ground into the ground of the gauges, it would mess up the gauges power feed because I would be varying voltage to the main power wire. If I wanted to use the stock dimmer for the new gauges, it would need to vary voltage on the + side, not the - side. What are my options?