There are X Format/Y Format properties, but I can not find any document at paco's web site.
http://www.um.es/fem/EjsWiki/index.php/Main/ElementsPlottingPanel

I have never used that before.
If I really need it, I will use drawingPanel  instead and I can draw those grid lines/labels with build in GUI elements.
May be it can be done by setting proper value for X Format, but I do not know. Sorry!