A very pragmatic way would be to click on AC PC as usual for one brain, this will generate
the file somethingIforget.APC in the folder of this subject. You can duplicate the file
for all the other subjects. You just have to change the subject name in the file name. For the other
subject you just skip the ACPC process.
Otherwise, you have to add an option in the brainVISA process, with the right coordinates
for AC/PC. It should be easy too.