I've got a one-way flight booked from LAS to LHR in PE, booked using 35k miles from my wife's Virgin account. This cleared out her account, and she's not going to be earning any more miles any time soon.

I've got just over 15k miles in my account (and again, no real opportunity to earn many more anytime soon). If a UC redemption becomes available for the flight I'm booked onto, would I be able to upgrade to UC using the 15k miles in my account (the difference between a PE and UC redemption for this flight), even though the flight was originally booked using my wife's miles?

Thanks for any replies!