like it was stated before.
its not impossible, but GCC, C++ etc will be rebuild, even when chosing only fortran.
This will create overlay packages of standard C compilers and libraries.
Now, a plausible solution is to rebuild, using exact same version that is in Jolla, but creating an install package, with only fortran.
Plausible, but not straight-forawrd, and may give issues still resolving conflicts, as a build fortan package on mer would still claim dependency on mer build of gcc, g++ etc.