I heard a story once that in acity with rat infestations, the government proposed a bounty for each rat-tail that could be shown as evidence of having killed a rat. Promptly the rat population increased exponentially.

If you made the race to salary, you can remove health benefits, PTO, stock, restricted bonuses, etc etc to artificially increase the number which would in the end harm the worker as well, since he will pay a higher tax rate for the shenanigan.