Some motherboards you can purchase an extra temperature diode on a cable that you can attach anywhere in the case, graphics card is generally the most popular.
But to get an effective reading you have the place the diode between the GPU and the heatsink so you would have remove it an re-attach, with some graphics cards this is a problem, cheaper ones are bonded on and difficult to remove...and to re-attach.
You can also get those LCD displays that go on the front, I would imagine they may have a similar cable and diode.
Jamie