I am not sure exactly where you're coming from.
What is the basis of your validation? Is it from a UK CPL? What ICAO licence do you have?
A possible way is to go back to the country who issued your ATPL, get them to issue you with a JAR one and then see the CAA.
I was under the impression that the validation gave you a year to then do the appropriate JAR exams. I haven't heard of someone getting a validation recently, before the UK went JAR there were a few foreigners flying over here on validations but they still had to do the UK CAA ATPL exams in that year Once they had the UK CAA ATPL (and all the hours) they could then swap it for a JAR ATPL (after paying a fee of course)
You don't need 1500 hours in command to get a JAR ATPL. Just 1500 hours based on the requirements as spelled out in LASORS. (CAA document). (PIC, Dual, PIC U/S, P2 all counted)
If you have a foreign ICAO ATPL with 1500 hours in command on +30 tonne aircraft with a total time of +3000 hours then that is a different thing. (You need to do 2 exams and get a check ride done with the CAA observing)
Not quite sure what the beef is with the European folk coming here to get their licence and go home again???