If you go and get an FAA multiengine license, I think you will still have to convert it over to a JAA by doing a skills test in the UK, and if you plan on doing your IR in a twin then this is a must. Why not just go out to the USA for a 2 week holiday and get your 50 houyrs PIC while you're there. I,m assuming you've got your Night rating and X-country qualifier done otherwise you can't get you're CPL issued.