Well, I have solved this problem with a kludge. I created a python script, cppcensor.py, in my $HOME/bin directory. This script simply goes through its arguments, deleting every occurence of ‘-L/lib64’. It then execs the actual c++ compiler (using an absolute path) with the censored argument list. I then symlinked this script to c++ in the same directory. ~/bin is in my path ahead of the actual c++ compiler, so the script takes precedence. This is ugly, but it actually solves problems I had in installing dolfin, too (Building from source: mpi4py, petsc4py conflict).
And, it seems to work!