Hmm... try to be more specific.
Where does user click? If you have a button you can simply use the ServerClick method and then it's also easy to save his selection.
You might also want to set the trigger in the UpdatePanel for your control to cause a postback or async postback if you have the "conditional" UpdateMode.
Or try Me.ScriptManager1.RegisterPostBackControl(myControl) in the Page_PreRender event.