If the secondary menu is specific to an individual page, and it doesn't have to have a hierarchy, you could try using the Links module on the page(s) that need these extra links. The client could edit each instance of the Links module to update it as needed.
If you need to keep track of a hierarchy of links though, or show the same set of links on every page (i.e. edit once, update everywhere), you'll probably need to develop your own custom feature to handle that. I was brand new to .NET programming when I started with mojoPortal too, but it was pretty easy to get started, especially when following the great documentation here, and looking at code samples within mojoPortal itself.