This is a topic that came up multiple time:
@John_Mosher, @Sylvain and @leahy decided not to implement this solution in Brainstorm.
It should be possible to access this method through the FieldTrip source estimation process (ft_sourceanalysis), but it would require some more coding/testing.
There are a few lines of code missing to handle it correctly here:
https://github.com/brainstorm-tools/brainstorm3/blob/master/toolbox/process/functions/process_ft_sourceanalysis.m#L147
Do you want to give it a try?