Thank you for contacting Telerik support.
The described behavior is not supported for Radmenu control, but it can be achieved by a custom additional CSS. We are sending you a sample prototype of a RadMenu where we show an approach or a direction how you can achieved pushing the content down.
Do not hesitate to contact us if you have other questions.
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?
Telerik Feedback Portal
and vote to affect the priority of the items