LH flys to KUL from BKK. it's not hard to find F seats on TG from Europe to BKK and either LH or UA seats to Europe from the US - then you can take LH to KUL (the only flight with F as all TG flights on this sector are 2 cabin
Something like this:
LH/UA/LX USA-EUROPE
TG EUROPE - BKK
LH BKK - KUL
Sometimes the LH flight is avail all the way from FRA-KUL but TG has much more availability. The LH sector from BKK-KUL is ALWAYS WIDE OPEN IN F