As I replied earlier, if you want to configure buttons by hand via buttons.cfg file, then you won't be using the FOP2 Manager at all. On the other hand, if you want to use the FOP2 Manager, you can setup the engine by hand in /var/www/html/fop2/admin/config.php , you can select "astdb" as the engine, however you will probably need to edit system.php and remove the place where it looks for freepbx config files, as it will reset your engine selection.
If you use the FOP2 Manager in astdb mode, then you might probably need to tweak functions-astdb.php so it reads the config files for asterisk you have defined for your extensions and such.