You dont actually need the ups. If you use a DC-DC power supply all you really want is something to plug in the usb that makes the computer think it has a UPS connected.
Then you can make use of the features - consider this:
You turn the car off and the message of "power off" is sent to the computer. Your machine is still on and powered by the DC-DC converter but will shut down in 10 minutes if the car isnt started and the "power on" message is sent to the computer.
A simple program could be written to mange this.
Edit: would also require a small amount of electronics.