To display the list of the bars on the popup menu you can use DotNetBarManager.ExpandedChange event to dynamically add/remove ButtonItem objects that describe the bars.

Sample attached below is modified DockableWindows sample that shows how to do that. Note that under Bars menu item there is a place holder item which is just a dummy item that will cause menu to be expanded and ExpandedChange event generated.

Sample application:
DockableWindowsListBarsonMenu