winhttp proxy user password

Hi to everyone,

my lan have limited users (they only can navigate in google sites) and
unlimited users (admin and software).
The software user is to set the antiviral definition and windows
updates up to date.
I can set the proxy doing:
netsh winhttp> set proxy myproxy.com:80
It works well but it shows the user/password dialog. This is my
problem. I've not found the way to remember the software u/p in the
limited user's computers. Obviously, Is not interesting to let the
"unlimited" user/passw to the other users.
hidden .ini file? reg key?

ideas?

thanks in advance!