Expiring URL Shortener

I'm looking for a site or a script that can shorten URLs with a time limit of a few days before they expire. I don't want the original referer of the link the user clicks on to be masked though. So they clicked on a link on yoursite.com I'd want yoursite.com to remain as the referer.

Does anyone have any suggestions?

I've found ephemurl, which is perfect except for the fact that it obscures the original referer. Other than that scripteen have a script that you self host and seems like it can do exactly this, however it flashes up a big ad before the user gets to the link I want them to get to.

Thanks!