afaics the original forum request turns out to be a misassumption about what "remember" does when "opening with..." -> the should or could be "add to associations" checkbox (even if that would be done automatically, just for disambiation)
a mounted media /is/ inode/directory, if you want to treat things differently you'd need sth. more advanced that inspects path or content and runs a special app in case. -> bash script + service file or write sth. with a nifty config gui.