How to disable session extends with Liferay 6, Vaadin 7.6.6

I am running Vaadin 7.6.6 Portlets in Liferay 6.

I noticed that when Vaadin does AJAX calls back to the server, a Liferay extend session AJAX call is also made. 
I traced it back in the vaadin base widgetset in:

function com_vaadin_client_communication_MessageSender_extendLiferaySession__V(){
  if ($wnd.Liferay && $wnd.Liferay.Session) {
    $wnd.Liferay.Session.extend();
    $wnd.Liferay.Session.banner && $wnd.Liferay.Session.banner.remove();
  }
}

com_google_gwt_lang_JavaClassHierarchySetupUtil_defineClass__Lcom_google_gwt_core_client_JavaScriptObject_2Lcom_google_gwt_core_client_JavaScriptObject_2Lcom_google_gwt_core_client_JavaScriptObject_2Lcom_google_gwt_core_client_JavaScriptObject_2(1131, 1, $intern_510, com_vaadin_client_communication_MessageSender$2_MessageSender$2__Lcom_vaadin_client_communication_MessageSender_2V);
_.execute__V = function com_vaadin_client_communication_MessageSender$2_execute__V(){
  if (this.com_vaadin_client_communication_MessageSender$2_this$01.com_vaadin_client_communication_MessageSender_connection.com_vaadin_client_ApplicationConnection_applicationState != (com_vaadin_client_ApplicationConnection$ApplicationState_$clinit__V() , com_vaadin_client_ApplicationConnection$ApplicationState_RUNNING) || !(this.com_vaadin_client_communication_MessageSender$2_this$01.com_vaadin_client_communication_MessageSender_hasActiveRequest || this.com_vaadin_client_communication_MessageSender$2_this$01.com_vaadin_client_communication_MessageSender_connection.com_vaadin_client_ApplicationConnection_serverRpcQueue.com_vaadin_client_communication_ServerRpcQueue_flushPending)) {
    com_vaadin_client_VLoadingIndicator_$hide__Lcom_vaadin_client_VLoadingIndicator_2V(this.com_vaadin_client_communication_MessageSender$2_this$01.com_vaadin_client_communication_MessageSender_connection.com_vaadin_client_ApplicationConnection_loadingIndicator);
    com_vaadin_client_communication_MessageSender_extendLiferaySession__V();
  }
}

We are using Liferay's auto session extend, so we would like to stop Vaadin from telling Liferay to fire off extend session (which takes up a not-insignificant part of our traffic) on AJAX activity.

Is there an easy way to do this?

Thanks in advance.