<asp:UpdatePanel ID="updPanel" runat="server">
    <ContentTemplate>
    ....
    </ContentTemplate>
    <Triggers>
        <asp:AsyncPostBackTrigger ControlID="the control" EventName="Click" />
    </Triggers>
</asp:UpdatePanel>

protected override void OnInit(EventArgs e)
    {
        AsyncPostBackTrigger trigger = new AsyncPostBackTrigger();
        trigger.ControlID = "the Control";
        trigger.EventName = "Click";

        updPanel.Triggers.Add(trigger);

        base.OnInit(e);
    }

Dim addTrigger As New AsyncPostBackTrigger
        addTrigger.ControlID = MyButton.ID
        addTrigger.EventName = "Click"
        MyUserControl.GetUpdatePanel.Triggers.Add(addTrigger)

var prm = Sys.WebForms.PageRequestManager.getInstance();
prm._panelsToRefreshIDs = UPComments.uniqueID;
prm._doPostBack(eventTarget,eventArgument);
theForm.submit();