How can I change media source for user photo

Hey guys,

as stated in my question I'd like to know how can I change the media source for the core user photo in the user management?

I am having a client account with access to a client-specific media source. The client has access to user management but when trying to add/update a user photo the media browser is always empty and throws errors because the client has no access to the default media source. I need to change this/assign the client-specific media source to the user photo in order to allow the client to change the user photos.

Any ideas?