Hello Oliver Abraham,
Please accpet our apology for the delayed response.
You can create a custom control with the required style, using the RadButton, RadDropDownButton and the RadWatermarkTextBox controls. You can edit the RadDropDownButton ControlTemplate to place a modified RadWatermarkTextBox with a RadButton placed inside its ControlTemplate.
I prepared a sample project illustrating a possible approach. Please have a look at it and let us know if it works for you or if we can further assist you.
the Telerik team
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