Ask HN: Has this been done? Cost-sharing for ads

Are there any services out there that allow people to share the cost of an online ad campaign -- I'm thinking specifically on Facebook, but possibly on other ad platforms?

Here's how I'm envisioning it:

A group of advertisers evenly split the cost of an ad campaign purchase. When users click on the campaign's advertisement, they're taken to a "splash" page that features separate advertisements for each of their businesses.

I know what you're thinking: How can you create an acceptable, enticing ad for five potentially disparate businesses? I think I've got that part figured out. I'm just wondering if anything similar has been done.