disablepasswordcaching in IE and regedit issue

In my environment, I am using group policies to lock down machines for
certain groups of users. Once of these restrictions is to prevent access to
edit the registry. I am trying to remove the "save password" box from the IE
Proxy authentication window with a registry entry. It works great for all of
my users except for the ones prevented from running regedit. Is there a way
to make this work while still locking down the machine? TIA