There have been multiple reports of success in applying certs for travel AFTER expiration as long as the upgrade space is available at the time of use and upgrade clears immediately (i.e. upgrade clears before expiration date). I was able to do this with GUCs expiring this Feb for travel in May.

If you have any trips booked after expiration date of your RUCs I'd give DL a ring to see if any of those trips have upgrade space available and try to use them.