I could be wrong, but I don't think you can. I'm not sure why because I have to do it daily. I do it through the sign up screen and use one of my many email addresses to fool Oxwall. Elgg has this feature and maybe I'm missing it somewhere here.

i been looking all over the place cant seem to find it..if its missing then we need it LOL

would really help adding new admins/mods quicker.

This can't be done from the admin panel, you need to register your new user via the front-end

You can make a suggestion on uservoice for the oxwall team consideration to develop it. 

Thanks ross for the fast replay