Hide roles not applicable to user type

When you are a certain role and you would like to create an account for a certain user type then all the available role check boxes appear as well so it makes the user type then useless. Can it not be made that if you create an account for a user type that you can only assign one pre determined role to that account. Also then if you create an account and assign a role to that account and you allow that account to create account s for other users that you can assign roles that the account can can assign to the new users it creates. In other words if you create an account for user 1 with role admin and role admin can create other accounts but he can only assign the role of subadmin to the new accounts he creates.