Here's what I would do...
1) Link in KendoUI
2) Create a custom layout control
to be your "container" (By default on live it's style is hidden). You can also just tell editors to give it a wrapper class, but I hate that idea, means they have to remember wrapper class names.
3) Create a new Widget to plop into that...perhaps it's designer just shows Title and Content. On render the widget dumps simple HTML UL\LI elements into the kendo preferred format. Title being the panelbar text, content being what shows when it's expanded.
4) On Live view (not design) you then Kendo the outer container.
5) Do a .show() to make the "panelbar" appear (so there's no popping of elements...perhaps its so tiny you wont notice any and this is a useless step)
Perhaps to be more fancy, the outer container accepts child layouts, and the immediate child layouts become the panelbar items...it'd be more tricky that way....but more flexible for content editors.
Should be LIGHTYEARS more lightweight and cool than those horrid AjaxToolkit controls