You could achieve your scenario with changing a little bit radGridView.EditTriggers flag enumeration. By default RadGridView starts editing after following actions (press F2, CurrentCellClick, TextInput). I think that if you set radGridView.EditTriggers = "F2, TextInput" you will get the desired result. That way RadGridView will not be able to enter into edit mode with a mouse action. Since this is a little bit strange for end users you can solve this with a few lines of code (just add a ClassHandler for GridViewCell.MouseDoubleClickEvent (or any event you find appropriate)). I'm attaching a sample project that demonstrates the approach with MouseDoubleClick event.
Let me know if this does not help.
the Telerik team