Sorry for not looking at this earlier. This is currently not handled by afni_proc.py. It has been on the to-possibly-do list for years, but has not had much demand.
What is your use case? I would think MIN_OUTLIER would be a very good volreg base. What are you using for that? Is it to get the volreg output into a different location? Are you not going to standard space?
Thanks,
- rick
