You can add a step to the link bar by adding a child to the
viewstack. Perhaps whatever it is you are popping up could be made
the viewstack's new child. Just be sure to set the label property
as that's what's used as the LinkButton label in the LinkBar.
var newchild:YourClass = new YourClass();
newchild.label = "Final Step";
viewstack.selectedChild = newchild;