How do I use a DataPager with Server Side Paging?

I'm trying to use a DataPager to do Server Side paging. Here is my code

<asp:DataPager ID="pgrFooBars" PagedControlID="lvFooBars" 
    QueryStringField="page" runat="server" >
<Fields>
    <asp:NumericPagerField />
</Fields>
</asp:DataPager>

Code Behind

protected void Page_Load(object sender, EventArgs e)
{
    ConfigureBlogPostListView();
}

private void ConfigureBlogPostListView()
{
    int pageNum;
    int.TryParse(Request.Params["page"], out pageNum);
    int pageSize = 20;

    PagedList<IFooBar> FooBars = FooService.GetPagedFooBars(
        new PagingSettings(pageNum, pageSize));

    ListViewPagedDataSource ds = new ListViewPagedDataSource();
    ds.AllowServerPaging = true;
    ds.DataSource = FooBars;
    ds.MaximumRows = pageSize;
    ds.StartRowIndex = pageNum;
    //TotalCount is the total number of records in the entire set, not just those loaded.
    ds.TotalRowCount = FooBars.TotalCount;

    lvFooBars.DataSource = ds;
    lvFooBars.DataBind();

    pgrFooBars.PageSize = pageSize;
    pgrFooBars.SetPageProperties(pageNum, FooBars.TotalCount, true);
}

PagedList comes from RobConery's useful post http://blog.wekeroad.com/2007/12/10/aspnet-mvc-pagedlistt/.

The problem is that the DataPager appears to be using the Count property of the ListView to determine the total number of records, which in this case is 20. Somehow, it needs to know that there are 1,500, not 20 total records. The DataPager has a property TotalRowCount, but this is read-only.

I have never seen a DataPager example with Server Side paging, but assumed that it could do Server Side Paging, otherwise what good is the QueryStringField attribute?

I am aware that you can do a custom paging solution using methodology like the 4GuysFromRolla did here asp.net server-side datapager