And yes, the check is marked "Account Payee Only". I have no idea what the implications of that sentence is
That scuppers the plan. In the old days, you used to be able to "sign over" a cheque made payable to you, by writing the details of the person you wanted to give it to and signing it on the back.
"I sign this cheque over to jollyrog, please pay him [signature]"
If a cheque is marked "a/c payee only", this is not possible. I must admit, it's a very old fashioned practice and clearly subject to massive fraud, so it's almost unheard of these days.
Plan B - why not call HMRC, explain your circumstances and ask them to cancel the cheque and pay direct to a UK bank account instead? I will give you my bank details, then send you whatever I get in cash, less the postage. Can't say fairer than that.
Worth a try, if you trust me.