My thought about SecurityAssist and adding an admin level... SecurityAssist wasn't designed to do that. My gut tells me that you'll never be able to do that with SecurityAssist. SecurityAssist does one thing very well. It allows one person access to the pages they've been given access....period.
I go back to creating a backend UPDATE/EDIT page that you place in a password protected directory. I would recommend using DataAssist, but if you are already over budget, then just use the regular edit option. You can use a query the looks for an email address. Select * from <table> where email = _$POST['email'].... Something like that. Then update the fields that you want to change.
The following is rough... But it's a good place to start...
You'll have to create a page with a <form method="POST" action="update_user.php"> and an <input name="email" value=""> to push your user info to your Update page.
That will get the job done.