Button That Performs A Server-side Action And Returns A File To Download?

I have an ASP.NET page (using ASP.NET AJAX and the Telerik RAD components) that provides a data table and an option to download data in CSV format.I have a requirement that a single button allow the user to download a data set. I have a system set up that's nearly working for me based off the solution in
http://stackoverflow.com/questions/104601/asp-net-response-redirect-to-new-window

<asp:Button ID="ExportCsvButton" runat="server" Text="Download to CSV/Excel"
byte[] csvBytes = someLongOperation();
Session[EXPORTED_SESSION_KEY] = csvBytes;
Response.Redirect("myexportpage.aspx", true);
protected void Page_Load(object sender, EventArgs e)
{
Response.Clear();
Response.ClearHeaders();
Response.ClearContent();
Response.AppendHeader("content-disposition", "attachment; filename=" + "file.csv");
Response.ContentType = "text/csv";
Response.AddHeader("Pragma", "public");
Response.BinaryWrite(Session[OtherPage.EXPORTED_SESSION_KEY] as byte[]);
Response.Flush();
Response.End();
}


This actually works quite well. When I click the 'Export to CSV' button, the page's UpdateProgress kicks in and my loading overlay appears (it's a CSS div that covers the window when visible). This can take some time depending on the data set (potentially several minutes), at which point I'm getting a window popup with my file.