g++ should be available. We don’t use the mpic++ wrapper, which is in the conda environment by chance rather than because we requested it. Can you compile outside the RSP and copy in the binary? Do you need MPI support even though you don’t have many cores on the RSP?
I am installing code that is not my own, so I’m unsure of how entrenched the MPI assumption is in compilation. It would be good to have MPI support, yes.