You could do the FAA Commercial then convert either in the UK or at one of the schools in Florida or back in the UK. There is no prerequisit of hours required for the conversion, its merely stated 'as required'.
I would suggest if you do them back to back then there would be no rustiness and you would potentially be able to do the CAA checkride without any further instruction.
So 2 MEP licences, less than the cost of a CAA one done in the UK. No weather issues.
Seems a simple choice to me.