[Freesurfer] wmparc.mgz average

Hi FreeSurfers,

I was wondering if it is possible to obtain an average wmparc.mgz file for a group of subjects that have been processed through freesurfer? We have 72 cases that have been independently processed through freesurfer, and we would like to generate a representative white-matter "atlas" that could potentially be aligned to some standard space (e.g., MNI). Would this be possible?

If this isn't possible, could we obtain this from fsaverage? I noticed that $FREESURFER_HOME/subjects/fsaverage does have an aparc+aseg.mgz --- is there also a way to get wmparc.mgz (e.g, using mri_aparc2aseg)?

Thanks in advance for any suggestions!

-Ryan Muetzel