Hello Mark,
You need to build a custom control that is bound to IList of ICms pages. The built in controls are bound to SiteMapDataSource control with uses built-in CmsSiteMap provider.
Another option is just append this link as a single separate menu item, so the you will have two controls which will look as a one - the first control will be show as it is now, the second control will show a single item - say RadMenuItem.
Sincerely yours,
Ivan Dimitrov
the Telerik team