Adding roles to add user wizzard

Hi I have seen a few posts where they have added a user role to create user wizzard but they all add loads of other stuff to the information the user has to enter I have the add user wizzard under an admin folder and by default the wizzard does not add a role to the user I just want a radio button or drop down box to add a role to the user when they are created

 how can I do this withough adding loads of new fields to the form

 thanks

mike
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