How to implement a WPF circular progress bar with a linear gradient brush

Question

How do I implement a WPF circular progress bar with the following linear gradient brush:

<LinearGradientBrush x:Key="LinearGradientProgressBrush">
    <GradientStop Color="Yellow" Offset="0"/>
    <GradientStop Color="Red" Offset="0.25"/>
    <GradientStop Color="Green" Offset="0.50"/>
    <GradientStop Color="Blue" Offset="0.75"/>
</LinearGradientBrush>

As the circular progress bar advances, the color needs to change at the end point of the arc, with previous arc colors staying the same. In other words, the Blue color wont start being painted until the circular progress bar gets to 75%.