Use sc-register-2.3.1 written by firstname.lastname@example.org. You can use it by installing sc-register and adding the following configuration.
(setq sc-load-hook '(lambda () (require 'sc-register))) (setq sc-preferred-attribution 'registeredname)
You will find it convenient when 'selection by completion' is tiresome, e.g., when including Japanese characters.
Note that sc-register does not work with Supercite 3.0 or later. It is said that sc-register will be integrated to Supercite in future.