Hmmm. The technique is not working (might be the translation to vb.net: here's what I have:

Public Class SitesHttpModule
      Implements IHttpModule

   'Lots of code not relevant to this discussion



      Private Sub Application_PostAcquireRequestState(ByVal sender As Object, ByVal e As System.EventArgs) Handles Application.PostAcquireRequestState
         Dim objContext As HttpContext = HttpContext.Current
         Dim resourceHttpHandler As ForceSessionLoadHandler = TryCast(objContext.Handler, ForceSessionLoadHandler)
         If Not (resourceHttpHandler Is Nothing) Then
            objContext.Handler = resourceHttpHandler._OriginalHandler
         End If
      End Sub

      Private Sub Application_PostMapRequestHandler(sender As Object, e As System.EventArgs) Handles Application.PostMapRequestHandler
         Dim app As HttpApplication = CType(sender, HttpApplication)
         Dim objIROSS As IReadOnlySessionState = TryCast(app.Context.Handler, IReadOnlySessionState)
         Dim objIRSS As IRequiresSessionState = TryCast(app.Context.Handler, IRequiresSessionState)
         If ((Not (objIROSS Is Nothing)) Or (Not (objIRSS Is Nothing))) Then
            Exit Sub
         End If

         app.Context.Handler = New ForceSessionLoadHandler(app.Context.Handler)
      End Sub

   Private Sub Application_PreRequestHandlerExecute(ByVal sender As Object, ByVal e As System.EventArgs) Handles Application.PreRequestHandlerExecute
         Dim objContext As HttpContext = HttpContext.Current
      'Code that attepmpts to access the session -- It's "Nothing" here
   End Class


   Public Class ForceSessionLoadHandler
      Implements IHttpHandler, IRequiresSessionState

      Friend ReadOnly _OriginalHandler As IHttpHandler

      Public Sub New(ByRef originalHandler As IHttpHandler)
         _OriginalHandler = originalHandler
      End Sub

      Public ReadOnly Property IsReusable As Boolean Implements System.Web.IHttpHandler.IsReusable
         Get
            Return False
         End Get
      End Property

      Public Sub ProcessRequest(context As System.Web.HttpContext) Implements System.Web.IHttpHandler.ProcessRequest
         Throw New InvalidOperationException("ForceSessionLoadHandler cannot process requests.")
      End Sub
   End Class