If I understand correctly, you have some number of chips to play with that were free, with no deposit required. But, you must play through 99x the bonus amount in betting action before you can cash out. Am I correct so far?
I don't believe your standard deviation will be substantially higher at this game because even with more splits and doubles, you only get even money on blackjacks. SD will probably be somewhat higher, but not by much. Are you betting the table max? If not, bigger bets are a more effective way to increase the overall SD over the required betting action. And regardless of the game, you MUST play the proper BS for the game in question or you are leaving money on the table.
One common strategy on these types of high-playthrough bonuses is to employ a high variance strategy early to attempt to either achieve a high target or bust (somewhat similar to a sticky bonus strategy) and if the target is achieved, then you would play out the required playthrough at a low house edge game like blackjack. Here is an example of how that would work, using a hypothetical fair coinflip game for the first stage:
Lets assume your account starts with a $100 bonus with no deposit required, but you must play through $10000 in betting before you can cash out. Playing BJ with a house edge of 0.5%, you expect to lose $50 of the $100, so your EV is approximately $50. (Actually, this isn't quite correct because it doesn't account for the times you bust before completing the required playthrough, but lets ignore that for now.)
Now, if we flip a coin and either bust or start with $200 in our account, our EV is 0.5*$0+0.5*($200-$50)=$75. By flipping a coin before starting, we've raised the EV by $25. This is because on average we are only giving $5000 in action at 0.5% HE, not the original $10000.
We can continue by flipping a coin twice, so we bust 75% of the time and start with $400 25% of the time. The EV for this approach is $87.50.
The point is that a high playthrough requirement isn't an automatic dealbreaker. It just requires a different approach. The approach is essentially to play a very high volatility game until you hit some target or bust, then if you hit the target, you play through the remaining required action and cash out a good profit.