What about giving them a high potential but making their actual salary a function of approval rating? In order to maximize how much you make you have to work to unify your constituents.

I don't think you'd want this to be linear either. My feeling is you'd want the pay to stay pretty low anywhere below a 50% support level and climb pretty steeply above that, which discourages the split people down the middle mess the US is in. You'd probably accept that a small portion of people are nutcases so the salary would approach the max at around 85-90% support.

There are some potential exploits that you'd have to try to address but it's a thought.