I've prepared a sample project to demonstrate how you can achieve your goal. Please find it attached and inform us in case you have any problems or concerns.
I would like to inform you that you are able to use RadContextMenu as a content of RadDropDownButton, so if you need this functionality, there's no need to use RadToggleButton. The code is shown below:
Hope this helps. Feel free to contact us in case you have any problems or concerns.
TRY TELERIK'S NEWEST PRODUCT - EQATEC APPLICATION ANALYTICS for WPF.
Learn what features your users use (or don't use) in your application. Know your audience. Target it better. Develop wisely. Sign up for Free application insights >>