I made with a switch on enum. i define the different states of the hud in the enum so that i can call them by name.
You then can make that enum public and set it from where you want to switch the hud.
Multiple DrawHUD-Nodes would be awesome. Like DrawHudElement nodes. I kind of tried to build a system like that. where you can setup screens from text and input elements
But i think with 4.4-5 when UMG is in an usable State might be obsolete.