Mikey, I see the route you're looking at and it's very tempting. BUT the reason I'm going to do my CPL/IR in the UK is the same reason why I'll not be going down the route your thinking of.
From what I have heard and read on this forum and having spoken to a couple on CFI's from US schools is that the difference between FAA and JAA and quite different. And it's back to the old line of
"If you want to work in the UK do your licence in the UK"
I'll be finishing work with my current employer after completing my ATPL exams to sit the CPL/Multi IR followed by a FI course. I guess the cost of an JAA CPL and FAA IR > Converted to JAA Multi IR and CFI MEI CFII in the states could be done a lot cheaper than the usual JAA route
Food for thought I guess - let me know how it goes Mikey