I contacted the UK CAA about this. I have a UK-issued JAA PPL (SEP) but live in the Netherlands. The UK CAA had no problems with a Dutch JAA examiner signing the paperwork, provided that a copy of his license was sent to the UK CAA along with everything else.
So just find an IAA JAA examiner, have him/her sign the paperwork, make a copy of his/her license and send it to Gatwick together with the rest. Sorted.