Hi there amou7,
I was in exactly the same situation as you a long time ago. I also had the LET410 on my TZ CPL. For me it didn't make any difference coz i ended up doing a JAA licence and when i got a job again on the LET in europe it was put on my jaa licence when i did my atpl checkride in Ostrava with LET's Fly.
Your options are this 1) Call LET's Fly speak to a guy called Martin Lubojacky +420 597471474 he is the owner ask him if he knows an FAA designated inspector that can do your FAA checkride.
2) Just go to Dar and renew your licence it can be a tricky issue because you have to do your IR. Can be expensive...
3) Do the full SA licence and get the LET on it and get your company to pay for it. The only thing is it will cost you a bit of time and money for the notes a good mate of mine did all subjects in 10 days but he was burning the midnight oil. It would make things easier for you and would probably be easier and cheaper than trying to find an faa inspector an going to czeck republic.
4) Please do send my Regards to Jean Luca if your'e flying with him
Hope that helps,
Pete77