how to disable mousewheel scroll with jquery overlay

Question

I have this code in a master page:

<asp:Content ID="Content1" ContentPlaceHolderID="head" runat="server">
    <script type="text/javascript" src="/Scripts/jquery.tinyscrollbar.min.js"></script>
    <script type="text/javascript">
        $(document).ready(function () {
            $('#scrollbar2').tinyscrollbar();
        });
    </script>
</asp:Content>

<asp:Content ID="Content2" ContentPlaceHolderID="rightContent" runat="server">
<div id="rightContentWrapper">
    <div id="sectionTitle">Investments</div>
    <div id="introText">Test Investments List</div>
    <div id="scrollbar2">
        <div class="scrollbar">
            <div class="track">
                <div class="thumb">
                    <div class="end">
                    </div>
                </div>
            </div>
        </div>
        <div class="viewport">
            <div class="overview">
                <div id="tombStones">
                    <%--  some scrollable images with overlays when clicked--%>                    
                 </div>
            </div>
        </div>
    </div>
</div>
</asp:content>

I have overlays that are invoked when someone clicks an image in the scrollable area. I want to disable scrolling when the overlay appears. To do that, in the onBeforeLoad and onClose of the overlay script, I hide the scrollbar and thumbnail at the top, which means you can't use the cursor to move the scrollbar. Here is that code:

<script>
    $(document).ready(function () {
        $("img[rel]").overlay({
            onBeforeLoad: function (event) {
                $('.scrollbar').hide("fast");
                $('.thumb').hide("fast");
            },
            onClose: function (event) {
                $('.scrollbar').show();
                $('.thumb').show();
            }
        });
    });
</script>

Unfortunately, in this scenario, the mousewheel still scrolls the scrollable area. How can I disable and re-enable mousewheel scrolling in my script to hide the scrollbar (or elsewhere)?

Thanks!