UI Slider; -x to +x range, 0 center; how can I get it to fill both directions starting from center?

Situation: I have a slider, with default value 0, and a range that goes from -5 to +5, with "whole numbers" checked; the slider is in it's default horizontal position. When the slider is at zero, half of it will always be filled (using either l to r, or r to l direction). This is what I am trying to get around. I would like for it to have 0% fill at 0, and to either go left or right depending on whether its handle is dragged to a positive or negative value. And now for a rudimentary ASCII example: For value +3, whitespace is no fill, - is fill, # is a notch in the whole number slider -5 0--- 5 Instead of: -5----0--- 5 Or: -5 0 --5 Anyways... I'm not really sure where to start, would love to hear your suggestions! Thanks PS: C# preferred... but I suppose beggars can't be choosers :)