yeah, what I used to do was set caster to debug which would result in me hosting but playing against myself. Spectators would join through my IP and observe. P2 would be unusable, obviously, but it would allow me to use it as a dummy of sorts to demonstrate combox/setups/movement/etc. And likewise, the observer could produce the same setup through debug and I could in turn watch them "practice" and would be able to correct their mistakes on the spot.
Having the option to just select training mode would make it a bit less annoying though (P2 dying and having to reselect characters, meter building issues, timer).