I might give a version of this a try SB. I just looked at possibly doing it in the following way:

Starting Bank $100

Each time you make profit equal to your starting bank ($100), 60% of that profit (instead of half) goes to a reserve and 40% goes back into the betting bank.

By my calculations it would take just 5 cycles before your reserve equals your betting bank and starts to surpass it.

Anyhow just another idea, i'm sure this could be tweaked in any number of ways.