Have a monthly pool for transactions you want to encourage. I would think buying steem/sbd from outside, transactions between users keeping steem in house, reward/prize distributions, and powering up would be encouraged. Give each kind of transaction some weighting/ranking value. At the end of the month each users gets: (weighted value of steem spent by user)*((this month's pool)/total weight value of steem spent))

This kind if scheme or similar would reduce the incentive to game the system while encouraging moving your steem around.