Depends on terms
I don't know what the terms of the "rebate on winnings" are. Is this a .5% addition to ... to what? Your buy ins? The amount you cash out? Cash out minus buy ins? Is there no rebate on losses?
What you could do, theoretically, is figure out your standard error (~0.67 x standard deviation) for a session, or hour or hand or whatever the rebate period is, and figure out your gain on the rebate alone from 1 standard error to the good plus one SE to the bad, and that is your average gain from the rebate. Divide by hands per period and add THAT to your .3 off the top.
But personally, I'd keep the old conservative bet ramp. If you're close to zero for a session, you may decide to bet high to snare the rebate, and that's going to add to your ROR.
ETF