I would replace the RadioButtonList with individual RadioButtons that are
wired to the same event handling method, e.g.
<asp:RadioButton AutoPostBack=True ID="Radiobutton1" Runat="server"
Text="value1" OnCheckedChanged
="Radiobutton_CheckedChanged"></asp:RadioButton>
<asp:RadioButton AutoPostBack=True ID="Radiobutton2" Runat="server"
Text="value2" OnCheckedChanged
="Radiobutton_CheckedChanged"></asp:RadioButton>
And in the codebehind:
protected void Radiobutton_CheckedChanged(object sender, System.EventArgs e)
{
//uncheck all radio buttons
Radiobutton1.Checked = false;
Radiobutton2.Checked = false;
//check the button that was clicked
RadioButton rb = (RadioButton)sender;
rb.Checked = true;
//do any other processing
}