You can simply turn off your Bluetooth on your computer, and that should unlock the built in mouse driver. However, as mentioned, when you do this you will lose your mouse cursor unless you have a hardwired PS/2 or USB mouse physically plugged into your computer. When the Bluetooth is turned off, your mouse cursor will still be there since windows will switch over to the hardwired mouse.
The other solution would be to buy a different keyboard-trackpad combo; such as ones that use wifi or IR. Bluetooth keyboards IMO don't work as well as the other technologies. With a combo wifi or IR keyboard-mouse device, disconnecting the device from the computer will usually leave the mouse cursor; on a desktop you still need to have a hardwired...