It depends on the bank, at some banks front-office developer bonuses are pay out of the desk bonus pool rather than a tech bonus pool.
There can be budgeting for specific desk profits in the relative bonus pools decided in IT, but bonus makes up a smaller percentage of developer total comp generally unless you are approaching management.
If you are desk dev and hack Excel and Access for the front office that can help your case in regards bonuses, but this isn't true software development of course.
Go to efinancialcareers and search for "PnL bonus" if you want to see some examples of job specs mentioning it.