Don't know of any US carriers that do, but as mentioned you would be at the top of the list to be moved up, if needed..... I've been upgraded a number of times by paying close to full C, over other "elite" members, primarily on DL, although it has been a few years now. Each airline has their own rules as to who to pick to move up, as needed. It is a combination of status, and fare basis. However, if they don't need to move you C->F (or Y->C) they usually won''t, unless you can support the upgrade with certificates/miles/etc...

The good news is that with full flights these days Op-ups are more common.... The bad news is that there are more elites requesting upgrades than in years past.....