Setting sticky bits for SMB share directories

I own a ReadyNAS Ultra. I'm trying to configure a SMB share so that new folders are created with permissions = 2775 (rwxrwsr-x). I cannot find any way to do this in the UI. Is there a file I can manually edit from an ssh shell on the NAS? I found Shares.conf but it sounds like that's overwritten each time the nas reboots.

In Samba, I'd normally just set:
force directory mode = 0775
directory mask = 0775

but I can't see a persistent way to accomplish that via files in /etc/frontview.

thanks!