Thank you for contacting us.
You can easily achieve this by editing the Header of the Window in Expression Blend. Just drop a Window in the design surface, right click it and choose from the menu Edit Template->Edit a Copy
. Then, Blend will generate all the needed resources. In that way you will be able to add your button to the header in the Border with x:Name="PART_HeaderButtonsBorder".
If you need further assistance please let us know.
the Telerik team
Do you want to have your say when we set our development plans? Do you want to know when a feature you care about is added or when a bug fixed? Explore the Telerik Public Issue Tracking
system and vote to affect the priority of the items