How do I detect a dual boot through a batch file

Here is my issue. I have employees installing dual booting on computers, effectively bypassing security software that is installed.

Is there a batch I can run to detect this, and output the results to a file ( on the network of course ) or something of that nature? I need a way to circumvent this ongoing problem, and I'm at a loss. Maybe a free program that is command-lined based that I can push through GPO? ( domain computers is one of the partitions ). I'm open to suggestions. Thanks everyone!!!

You might ask at Technet which is more IT oriented than our consumer forums. However someone here may also know exactly the commands you are looking for. Until then I have some considerations from an install point of view:

C can be shrunk and an OS installed from Win7 unless it has an Admin password which won't allow any changes without password being supplied.

Then the employee workaround would be to boot a partition manager or Diskpart to shrink C, then boot the installer itself to install another OS to the shrink space. But on some PC's a BIOS Supervisor password can be created in BIOS setup to restrict changes made to the BIOS. You'd have to test on each PC model if this also restricts the one-time BIOS boot menu key, which may have a setting to disable in BIOS setup so that disks can't be booted from within BIOS or by its shortcut key.