I haven't had to do this yet but what happens if you try to handle it from Main, do CreateScene again for the new screen when it's needed? (trigger that in Main with an observer on a field that gets set by the login scene)
Otherwise I could suggest having the OverhangPanelSet as the only scene and the login built as a component inside its XML, it can appear separately from / before / on top of the panelset.
aspiring