A cleaner way to fix this is to create an environment variable PROJ_LIB pointing to the right place.
This can be done by creating a file $env:CONDA_PREFIX/etc/conda/activate.d/env_vars.ps1 containing $env:PROJ_LIB=<CONDA_DIR>/envs/wmpl/Library/share
(where conda_dir is the conda root as indicated in the readme).
This should avoid having to repatch the distribution should basemap be updated.