Will UBS’s rogue trader leave staff with a “doughnut” bonus? The investment bank’s employees, already facing thousands of job losses, fear the $2.3 billion trading loss will wipe out this year’s payments. Loading the cost onto staff could appease shareholders and regulators, but would risk triggering another exodus. Clawing back deferred bonuses from senior staff might be a better way to spread the pain.

Before the scandal struck, UBS’s investment bank was on track to generate revenues of about 10 billion Swiss francs this year, according to JPMorgan. If it paid out a similar proportion in variable pay as in 2010, this year’s bonuses would have added up to about 1.9 billion Swiss francs. Further payments would have been deferred to future years.

UBS could choose to load the entire cost of the scandal onto its employees. After all, shareholders have not received a dividend in years. But this could prove counter-productive. UBS slashed bonuses in 2008 following massive subprime losses, only to suffer a staff exodus that left it poorly prepared when markets rebounded in 2009.

A better idea might be to share the pain between employees and shareholders. If the bonus pot was halved to around 1 billion Swiss francs, the bank’s overall return on net asset value would plunge to 7 percent, from 22.5 percent last year, according to JPMorgan. In that case, UBS’s investment banking division would make a pre-tax loss of around 400 million Swiss francs for the full year.

Such a loss would have a silver lining, in that it would allow the bank to claw back some of the 907 million Swiss francs that UBS is already due to pay in deferred bonuses in 2012. UBS can’t grab the entire amount: only the bank’s executive board, 200 “risk-takers and controllers”, and those paid at least 2 million dollars or Swiss Francs a year have “clawback” clauses in their contracts.

The clawback, which is subject to a sliding scale, would not make good the loss. However, it would send a signal that senior staff share some responsibility for the scandal. UBS executives have reassured shareholders and regulators that the investment bank had tightened up its risk systems. Given the now-obvious shortcomings, it is only right that they should share the pain.