If the AME won't give you two certificates, go to another AME, plenty of others will.
As you have a UKL CPL you also have a UK PPL, so why change it to a JAA PPL?
Yogi-Bear
There is no need to go back to the same AME again, you can go wherever you like. Once you have held a Class 1 there is no requirement to go to Gatwick ever again to get another Class 1.