Yes, there is a way to do this. First, let me give you some background.
Since all meta fields are automatically saved and set by Sitefinity, there must be some procedure how Sitefinity can do this automatically. The logic goes like this: Sitefinity looks for all controls that have id of a meta key and that can be cast to ITextControl interface. The importance of ITextControl interface is that it mandates the control to have a text property, so Sitefinity always knows that the value of meta field will be stored in controls Text property, without actually worrying what kind of a control it is.
Your problem is that RadEditor does not implement ITextControl interface and here is the solution:
1. Create a user control.
2. Drag RadEditor control on the User Control.
3. Implement ITextControl interface on the User Control.
4. Implement mandated Text property on the user control. In the get accessor return RadEditor.Content, in the set accessor set RadEditor.Content to the value.
5. Replace the textbox with your user control.
6. Set the id of your user control to the meta key for which you wish to use it.
I hope you'll find this information helpful. Thank you for getting in touch with us.
the Telerik team