There is currently a bounty running that would also provide a solution for mine problem as well. The current organizer awards 50. If I would award the same, this probably would motivate more people to work on this question.
Currently "start a bounty" seems getting not available if the bounty is already running. I would propose to replace it to "join the bounty" or the like, offering increased additional award for solution.
This possibility would also allow to contribute awarding only few reputation points (2 or 5, for instance), still adding more motivation to contribute the answer.
This makes sense in cases when the bounty task needs more time to solve so the reward is actually the price for work, not for attention. In such cases offering the second bounty with the same or comparable reward does not make any sense: if you offer the salary too low, you may not find the worker through ages.