This question is similar to Collaborative Answers/Point-Sharing but I'm thinking more specifically about sharing reputation from an awarded bounty, where the person who receives the bounty has the option to share a portion of the bounty with another user(s).
By way of example, I received a bounty for re-iterating another user's answer. I gave verbal credit and a link to the original answer but I would have shared some of the bounty if I had the option.
EDIT: Another example in a new comment to this popular question about dog paws. (It's a new comment, so you will have to expand the comments to see it).
"I so wish I could split the bounty, because there is clearly more than one answer here deserving some; but for the lack of that ability I'll just go with the highest-voted answer"