New PM upon Usergroup Promotion

I have usergroup promotions on my site, and I was wanting to know if there's a hack out there that allows you to auto-generate a PM when a user is promoted to the next group, and where you can customize the PM that tells the user the new features they get. I've seen this on other boards, but not on any vB boards. I searched at vB.org, and I saw a thread where someone was requesting the same thing, but never found a hack for it.