I haven't come across any communities that do this though it might be an interesting idea to implement.
However, not all of your key members might want to take part. One way you could give back is creating a premium user group which anyone can buy, then give these specific users access to that user group for free. This user group could offer things like an ad-free forum experience.
Just a thought, with the above everyone can take part and most likely will. With ad sharing, not everyone might be interesting in going through the process of getting setup. Not to mention it would be easier to implement / manage.
I was thinking just dedicating the option to article-writers we have already. They do it for nothing. To share their skills. So thought it'd be a nice surprise for them. Id help setup their accounts and whatnot.
I had something similar a while ago on VB where they simply entered their Adsense id in their profile and got a share. Can't remember how i set it up mind and it was questionable at the time whether it was in Google tos.