ek122,
From what i have read on the recent posts, you can only do that through the shell command. there is no GUI application currently available for you to. I'm currently in the same situation except i use a 500gig ext drive and I don't always need to have it automount r/w. There are instructions in the previous posts that will help you manually make drives either ro or rw.
I hope one day someone can provide a gui app that will do what you described. Much like the the features in NTFS-3G/Linux.
