By default, the RadioButton, CheckBox and DropDownBox controls are not Javascript controls (like the List control, for example) and as such, you can't call methods on the control to repopulate the choices shown in the control. You can however specify that these controls should be rendered as Javascript controls (which will then allow the choices in the control to be set using the control's .populate() method).

In this video we show how a RadioButton control can be rendered as a Javascript control.

Download component:
http://alphamediacapture.s3.amazonaws.com/videos/radiobutton_javascriptControl.zip