I was in a similar position...
I flew and lived in the US for 11 years, ending up as a CRJ Captain for a big regional airline. I did all the JAA tests and got the ATPL with a JAA CRJ rating in it. I applied for a couple of jobs in the EU but never got hired anywhere with just a CRJ/CL850 rating, my wife was keen on coming back to the UK for the kids school/family etc. so we came back. I commuted to my airline job for a while back and forth across the pond and finally realized that that was no life, so I applied and got hired a sim instructor at a big ATO in the UK, I'm 25 mins from home and got a nice new 50k Biz jet type on both my FAA and EASA licences and pretty happy with my lot at the moment.
My advice for what it's worth is to get the airline experience over there and try and get into a useful type (NOT a CRJ). Try and get a PIC E-Jet rating and then eventually a 73 or 320 rating, once you have all that, coming back would be a lot easier. Choose wisely though, get your command time in the regional ASAP if poss and then get out, in fact you should be able to get hired at most if not all majors or nationals without regional command experience (do you have a degree?).
If you're anxious to get back ASAP, go for an regional E-145 operator (I recommend ExpressJet/ASA) which as you know is a the same type as the Legacy, get that on your ATPL and a you might find a bit of work over here.
Good luck to you, feel free to PM for more info..