XP - remote assistance when remote computer has two monitors

I frequently use XP's remote assistance to work on remote XP computers.  More and more of our users are going to dual monitors, and when I remote to one of them, I get to see the display from both their monitors compressed into the remote assistance display on mine.  It's better than having to drive several hundred miles but just barely.  Does anyone have any tips that would allow me to see just their primary?

Our users are locked out of Display Properties, so just changing it temporarily is not an option.

thx