Anyone been successful in upgrading MPM fare ?

Has anyone ever been successful in upgrading a miles plus money ticket with miles, either before travel or at the airport?

If so how much did you have to pay ? In particular I am thinking that we could upgrade the ticket from K to an S , and then use miles (20k miles each) to upgrade to UC.
I am able to upgrade to UC MPM tickets one way, but it'll cost an extra £2054... ouch !

Thanks
L2H

[Pete]

Once, but it was strictly against the rules and it was Virgin's airport manager that eventually had to authorise it (and only because they had really let down our party on an unrelated matter).

Pete