This past December (December 28th) UA cancelled my flight from MEM to ORD. I was flying ORD to LHR on UA as well. I was able to get on a NW flight to ORD and then connected to my UA flight to LHR. I had paper tickets, but had to have them 'endorsed.'

This endorsement consisted of a handwriten "Rule 120" in ink by the UAx agent. The ticket was accepted with no problems, a NW BP was issued and I was upgraded to First Class (I am a NW Gold.) The fare basis was a non-refundable, discount economy (H or W fare basis if I remember correctly.)

All in all I was amazed at how easy it was to get the ticket endorsed (why can't someone just write "Rule 120" on the ticket themselves?)

Couldn't you just do it yourselves and get on a flight of your choosing, bypassing the UA(x) agent?