This *seems* like it should be possible. I created a small nas share which appears to be mounted on the system as /shares/misc. I can tell this by tests.log. I uploaded my firmware images and using the cli - i jumped into the adaptec command line utility and typed:

romupdate 1 /shares/misc/as5124

That should be all there is to it. But the utility says the file does not exist. Am I missing something here?