Update tooltip asynchronously

I know I can update the text a tooltip in the onBeforeTooltip method, but the tooltip won’t display until this method has completed. Is there a way I can refresh a tooltip while it is open?

So for example, if I have an event ‘ev’ with ev.participants = ‘’. The tooltip template contains ev.participants. Then in onBeforeTooltip I make an asynchronous AJAX call to fetch some data to update ev.participants. Once it is loaded, can I refresh the tooltip so the fetched data displays?

You could try to put some container to tooltip, save link to it somewhere and then after loading data put needed html to this container.
Or you could try to get tooltip DOM element with following code and put your HTML here:

scheduler.dhtmlXTooltip.tooltip.innerHTML = "Test";