Unfortunately in older versions the expand image is part of the root element and can't receive separate clicks. You can inject an element in each expandable/expanded element on pageLoad or RadPanelBar's OnClientLoad and adapt the KB article to use that element.
the Telerik team
Do you want to have your say when we set our development plans?
Do you want to know when a feature you care about is added or when a bug fixed?
Telerik Public Issue Tracking
system and vote to affect the priority of the items