Jxc,
If you did the FAA IR, you could then with an N registered aircraft still fly in the airways to Europe. I know the DOT were trying to clamp down on N reg aircraft based in the UK but to my knowledge this hasn't happened. If you did then wish to go commercial the FAA IR can be converted by then taking the relevant JAA exams, 15 hours additional training and skills test.
In answer to your question you could do your IR in another European state, there seems to be enough people doing IRs in Spain (another thread regarding standards).