'Use special form during user creation'

def get_form(self, request, obj=None, **kwargs):

    defaults = {}
    if (obj is None):
        defaults.update({'form': self.add_form, 'fields': admin.util.flatten_fieldsets(self.add_fieldsets)})
    defaults.update(kwargs)
    return super(UserAdmin, self).get_form(request, obj, **defaults)
