Assign parent category at user registration

OK, after days of searching I can’t find anything close to this. Anyone have any ideas?

I’m using the plugin Symbiosis, which creates a category in the user’s name when they register (let’s call it user_name_category for now), and all the user’s posts automatically go under their own category.

What I want is to have a dropdown box of select categories on the registration screen for the user to chose a parent category for their own user_name_category to be assigned to. If the parent category they want is not listed, then another input box would allow the user to add it to the selection of parent categories to choose from in the drop down menu. There are, of course, other higher level categories which are not meant to be part of the parent category list so these need to be blocked from the list.

Does anyone know if such a plugin exists?

Thanks