Alternatively, if the RadCircularProgressBar control's out-of-the-box functionality is not desired, a similar behavior exists in another one of our controls, more specifically, in the RadBusyIndicator control's Style for Crystal theme. The RadBusyIndicator contains a RadProgressBar with a custom ControlTemplate that can be used to achieve this requirement.
With this in mind, using the control template's version of the RadProgressBar, which is present in the RadBusyIndicator for the Crystal theme the following result is present:
With this being said, I have attached a sample application for you to test that contains the code from the above GIF. It is built with the NoXaml version of our assemblies in mind.