Can you be more specific of what needs to be implemented? Or maybe it would be easier if you discuss directly this with Martin.
"A set of ROIs or a spatial basis set, in the same space and resolution as the MEG data, saved as a nifti" . How do I obtain the latter using brainstrom ?
This is not something you would get from Brainstorm, but from FreeSurfer or any other T1 segmentation pipeline: FsTutorial/AnatomicalROI - Free Surfer Wiki
(the volume version aparc+aseg.mgz of the Deskian/Killiany atlas)