Thank you for contacting us.
The RadJumpList control does not support such functionality out of the box. My suggestion is to edit the ItemTemplate of the jump list to display the items of the groups in a ListBox or similar control. I have attached a sample project that demonstrates how this can be achieved.
I hope this helps.
Check out the Telerik Platform - the only platform that combines a rich set of UI tools with powerful cloud services to develop web, hybrid and native mobile apps.