Hi Ken,
Before you decide to go through the trouble of offering rake back and draining your own income, please look at this thread
http://www.casinoaffiliateprograms.com/bb/showthread.php?t=5975
and this one
http://www.casinoaffiliateprograms.com/bb/showthread.php?t=5750
and to Brad from Royal Vegas Poker:
All you need to do to stay competitive against places that offer rake-back is to incentivize your larger players. They are the ones who are tempted. Some rooms have decided to offer rake-back on their own – no affiliate involvement – to their larger players. But an incentive by any other name still does the job.