Wheels up,
Why don't you do the ATPL writtens in CZ or the Slovak Republic? You have the LET rating, I guess? Use the sim here for the ATPL ride. If you need a UK licence after, it's a straight swap.
A licence has to be done under one auhority, so if your ride is for initial ATPL isssue, you need a UK JAR examiner, however if he is willing to travel with you and is rated, there should be no problem.
If you are adding a rating to an existing licence, this is a whole different story and can be done in any JAR country. It does not matter wether this country is member of EU.
Ask the TRTOs directly regarding hours needed.
cheers, IP