I'd endorse what outside loop said there because I did something rather similar to what you're proposing there. I took an FAA IR whilst out hour building in Florida in a Warrior. Logic behind this was that I could then simply get an MEP and a 15 hr conversion course, then take the test to acquire a JAA ME IR. This was terribly clever in theory as it would save a lot of expensive UK ME training hours.
The flaw was that I like most people need hours in an aircraft not merely to be able to tick a box on the form but actually to build up sufficient proficiency in that aircraft to take the test with confidence.
So in the end I trained for longer than the 15hr minimum, partial'd the IR and came out roughly even financially as if I'd done it the normal way. It didn't help that I didn't fly at all for 7 months (doing the ATPL groundschool) between taking the FAA IR and starting the MEP and JAA IR conversion.