Well I guess your wallet address or a signed message doesn't matter once your bitcoin is with an escrow. But do any escrow people on this forum know how to make sure a ukash code is still valid? Better yet would be if the escrow could convert my code to a new currency, then they'd have a new code that nobody else knows to give to you once you've paid them.
I saw somewhere recently UKash vouchers are renewed when spent, so if I were to spend a few pennies to buy something online then I would receive a new voucher with the remaining amount.
I couldn't find any Bitcoin escrow services. Localbitcoins has escrow built in which would work.
As I said before, I am looking for someone (trusted) to buy a large volume of USD or GBP vouchers.