Any specific reason for requiring the bonus to be played on the 2x payout setting? It's the same +EV for the player no matter what the multiplier is, so why not let people play with more variety?
People are less patient when it comes to dealing with near 50-50 odds and wagering. The right strategy (to decrease variance overall) is to bet as little as possible to have the rolls distributed evenly towards the 99:1 edge trend line. But as most people wouldn't want to bet .00000001 BTC consistently over a long period (for the max bonus of .1 that is literally 300,000,000 rolls that you have to go through). Assuming 1 sec/roll which is very generous, it will take nine and a half years to complete the bonus wager requirements. It's just a profitable decision from a business standpoint and even as I point this out it's the inevitable truth: no one wants to spend that time rolling dice.
I am participating in this bonus, though. Will be doing a similar strategy, but wagering much higher.