FOP2 auto configuration scripts read a local database, they won't query anything in a remote server. So the easiest way is to add buttons by hand in the file /usr/local/fop2/buttons_custom.cfg
There is one caveat, as this buttons won't be part of any groups, you won't be able to use group filtering. So in order to see them you will have to edit any FOP2 user you have and uncheck all groups (that means it won't have any group filtering, and buttons defined in the above file will be shown).
