I'm not sure about your idea. I'm looking at it from the standpoint of my clients and the ones that even bother to do any
PR work at all usually do it in-house. Most of my clients can't even be bothered with PRs in general.
One of my advertising clients also has a subcontract
PR guy he has "employed" on-call for the past 3 years, a term I use very loosely since the
PR guy hasn't been used.
If you were going to make it fly, you'd probably need a creative hook to promote it. I have absolutely no idea what that would be though.