This sounds like we're tackling a symptom not the disease. Instead of figuring out how to stop bankers from being paid so much in bonuses, we should answer ask why a few times.

"Why can banks pay their employees so much?" - because they make so much money, and have so few employees.

"Why can banks make so much money?" - I'm not sure but it seems like banks can take risks, but pass off the real risk to others.

"Why can banks take risks, but not have to worry about the downside of those risks" - ...

I think if you follow that train of thinking you'll get to some structural problem in our current system. It doesn't seem like there is an easy fix here.