I tried to use a regex, but it did not work. There are different dialects of regular expressions. To use such an expression, I would need to know at least, which dialect you used in your app. You developed the app after all, so you should know something about regex, at least what regex library you used.
I have paired a folder like /mnt/sdcard/xxx on my Android device to the Dropbox root directory. So the remote path is /. When I exclude /mnt/sdcard/xxx/yyy/zzz, as you describe it on your help page, it does not work, while using /yyy/zzz works. Do you have an explanation for that?
Best Regards,
Gerhard