Round Slider (Circle shaped slider GUI control)

Are there any GUI examples that creates a round slider control sort?
By slider I mean ones like this
http://docs.unity3d.com/Documentation/ScriptReference/GUI.HorizontalSlider.html
To get an idea of it, here’s some demos of what I’m looking for
http://anthonyterrien.com/knob/

you should use 3 filled circle images. 2 big ones, one in grey, one in blue for example and one smaller filled circle in white.

Generate UI images for all 3 images. Set the image type of the grey and the blue circle to filled, type: Radial 360.

Put the blue cirle above the grey circle and the white circle above the blue one in the middle.

Now play with the fill amout of the blue one. I think that is what you want.