How about you don't use Sourcebans, and instead use the good'ole adminsimple.ini file we used to use in ZPS to add admins and whatnot?
Ideally the flags you would use on SB are the files on the server, and as long as you have the custom flags set up correctly you can just add donators to the adminsimple.ini file and give them 1 immunity and the custom flags + voting flags or whatever else you would want.
If you read the whole thread instead of skimming you would have seen that I mentioned that death tried that very thing Pillz. Sourcebans ACCESSES those files, and anytime it syncs up or w/e with the server it resets it. Hence when Death tried it once it worked, but a little while later suddenly it didn't work anymore.
I'm pretty sure that any time you update anything for admins who are on ZM, it updates that file. Dante was missing the models flag and so I went in SB to add it to his account, and when I looked at the adminsimple.ini file on the server afterwards, it had that custom flag listed.
If I were to disengage ZM server from sourcebans COMPLETELY it could work, but in doing that I would lose the good ban tracking tools we have, that allow us to identify players with past bans anywhere on CG, which is worth way more than the donator thing.
Noo, I've had admins on the ZPS adminsimple.ini file for years, Sourcebans never overwrit it; until the reinstall I still had Slywilliam, Sejo and Krolin listed in the .ini file. Perhaps ZM does it differently but from what I see SB doesn't use the adminsimple.ini file at all, and on other servers the file is empty because they add admins with sourcebans; but idunno.