15% for state taxes to get to 45%? 15% seems a bit high. Even in CA and NY, where the highest marginal rates are that high, I doubt that the bonus withholding is that high (but could be, I don't know).

I have used 99 for s w-2 before, but I don't think that will help you on a bonus check. Different rules and w-2 withholdings are ignored I think, but maybe 99 works? Not even sure if marking exempt would work.

Talk to HR and ask them how you can have less withholding. If it doesn't work by a w-2, they might be able to take written instructions if they aren't dogmatic about it.