The forecast says (for more than a year): "New 2D Features [...]Panel buttons animate on touch."
It is not implemented, yet. There are several other possibilities, though: Use pan_setbutton, as Rei suggested, or create view (sprite) entities with frames or use a digits element with a font that consists of your button frames covered by an invisible panel.
"Falls das Resultat nicht einfach nur dermassen gut aussieht, sollten Sie nochmal von vorn anfangen..." - Manual