Cool idea. If my logic is correct, having 5% of the bankroll will nullify the effect of a house edge. Anything more would mean +EV.
On the contrary, owning 5% of the bankroll usually means you get 5% after the house cut. I'd estimate it to be about 20%, meaning that you'd only get 5% of 80%
Well thats does depend on the casino i know of a few that give most the edge to the investors.
Bitvest being one of them its 1.7% edge investors get 1.15 and site gets 0.55% the rest is based on how much is lost and your share of the investment.
Then again you have to read sites carefully because some take the full edge on investment based gambling sites as a fee.
I'm pretty sure this could be a universal game plan tho i tried it with dice, plus there is other methods that can be stacked with this to get even more back out of it.