The makefile of syncgrain~ links statically with flext.a, so dealing with ld.so.conf is not necessary if you just want to run syncgrain~. However what about moving libflext.so etc. so /usr/lib? I don't see a real problem with doing this, it would solve some installation hassles and libpdp does the same. AFAIK there is no other libflext already in /usr/lib on common Linux systems.
Oh, i think it should be in /usr/local/lib, which is also the default for the new build system.
T