driver restricted to installed id only?

I've got a Kensington Expert Mouse. It's a USB mouse with a PS/2
adapter.

I recently acquired an IOGEAR KVM and am trying to use the Kensington
mouse with the KVM. It attaches to the KVM via USB, and downstream PCs
see the mouse as USB or PS/2 depending on the KVM adapter cable. When
the downstream PCs use the mouse over USB, it shows up as a HID mouse
with the KVM ID as the device ID (Linux probes show the KVM's vendor
name and everything).

The mouse works fine but since it doesn't show up with a Kensington ID
the Kensington drivers won't match up with the mouse. In particular,
the driver tool won't let me load the Kensington drivers because the
device is not supported by the drivers (presumably this is because the
USB device ID is not in the inf file, but I'm just guessing).
Furthermore, even though I can install the drivers with other mice (or
by installing while the Kensington is directly connected), the
"Kensington" manufacturer branch is not displayed in the device driver
manager.

My guess at this point is that I need to do something to tweak the INF
file so that it will match up with the mouse's USB ID. Anybody know if
that's correct? If so, what steps should I take?

Thanks