Datatable with url proxy and progress bar

I want to use a custom url proxy object in datatable in combination with a progress bar. But i cannot get it working, because the load functionality will be immediately called at initialization. At this moment the datatable wasn´t extended with the progress bar cause it can only be done in the next line of code.
I did attach to the onBeforeLoad event to show progress bar.
Snippet: Code Snippet

you can ‘auto’ extend ALL datatables with this code

webix.extend(webix.ui.datatable, {
  showProgress: function(){
    return, webix.copy(this.config.progressConfig||{}));
  hideProgress: function(){
    return, true);
webix.extend(webix.ui.datatable, webix.ProgressBar);

and no need to call showProgress / hideProgress explicitly

Thank you very much.