XPS13 Disable touchpad when mouse is attached NOT WORKING

The trackpad/touchpad works fine when it's set to always be on, but it is a terrible bit of technology so I don't want that. I want it on only when I'm not using a mouse...as a last resort if I just need to check something real quick. So I want the touchpad to only be active when no mouse is attached.

The XPS13 L322X ultrabook (and almost every other computer) is supposed to have this option available.  It exists as an option in the Mouse Properties.  Just click the picture of the mouse and you can see it there to "disable touchpad when USB mouse is detected".  So I selected it, but it doesn't work.  It just disables the touchpad completely...that is, when this option is checked the touchpad is disabled whether a mouse is attached or not.  When it is unchecked the touchpad works normally, but is always on.

Of course I updated the drivers for the touchpad (AND everything else) and made sure ALL my Windows 7 updates were up to date.  Changed nothing.  I looked in my device manager and saw two other HID-compliant mouse items when my USB was NOT attached, the option was ON, and the touchpad NOT working.  I don't know what those devices are supposed to be, but maybe they were casuing a false positive in USB mouse detection.  After disabling them, the computer still couldn't detect that there was no mouse attached and so should activate the trackpad.  Disabling them prevents the trackpad from working, so they ARE clearly necessary for the trackpad itself.

This contingent functionality is actually very useful, but completely broken on this computer.  And of course nobody from Dell has been willing or able to address the issue for over a year now.