To follow up, we were eventually able to make GL 9.2A run on the NAS by disconnecting the mapped drive, using the mapped drive letter for a temporary location outside the NAS to install to, then copying the files over onto the NAS and re-establishing the original mapped drive connection. Not pretty, but there were no other options that I could see which didn't involve replacing the NAS.

Some system file edits were required to fix the UNC path, but once the process was completed the program is up and running. The site is GL-only, so keep in mind that the process could have been more complicated with more than one active module in the system.