I haven't tried anything.... allot of peple have removed the rear wiper completely... but I would think that it should be as simple as conecting a proper resistor in the wire that feeds the small motor that moves the rear wiper or maybe a varible resistor if you want warible speeds.
My recommendation: do 2 applications of RAIN X (yellow bottle) and then forget about using the rear wiper, or remove it completely. In all my many Insight miles, I never found a need for the wiper. With the rain-x, the wind just blows the water off....
Using a resistor will slow the motor down. It may also burn it out.
The motor in the front has an extra switch that communicates with the intermittent relay circuit. In theory one could put a relay in series with the back wiper. It's coil could be powered up by the output of the front motor controller. The problem arises when the rear wiper and back wiper travel at different speeds. The rear wiper would then cut off at various points in its travel. Depending where it stopped this could hinder rear vision.