Since build 2852 it's possible to use action: "Bubble" for row headers as well:
dp.resourceBubble = null;
dp.onBeforeRowHeaderRender = function(args) {
args.row.data.bubbleHtml = "Test";
args.row.areas = [
{right: 0, top: 0, height: 12, width: 12, html: "!", action:"Bubble", bubble: new DayPilot.Bubble() },
];
};
You can get the latest build in the sandbox:
https://javascript.daypilot.org/sandbox/