This question: Delinking bounties from privileges - spent bountry rep should regenerate over time in proximity to my own badge request made me think of a possible alternative.
I agree with the down-voters of the first question that this is not a good plan for the site. However, better badges for offering a bounty might be useful, without breaking the system.
I propose a silver and gold badge, each based on total bounty offered and percentage of reputation offered as bounty.
For example, one might get a silver badge for offering 500 total bounty and total bounty amounts to 25% of reputation at the time of offering the bounty. Gold could be perhaps 2000 and 25%.
This should serve to reward users with at least moderate reputation who are generous with their bounties, without being devalued as automatic badges for every high-rep user.