Comment 56 for bug 133567

Actually, I guess hal needs to be updated.

There should be an <append key="volume.mount.valid_options" type="strlist">usefree</append>

around line 181 in 20-storage-methods.fdi

Once that's there, then you can use "usefree" in values for the gconf key /system/storage/default_options/vfat/mount_options