As far as I can tell this can only be done from within an ImageSpaceModifier script, but I don't see how that can be useful at all, because I want to apply them from Quest and ActiveMagicEffect scripts... you know, the kind that are actually able to do something because they have an event that happens by default, whereas the rest of the game's script types HAVE NO WAY OF EVER DOING ANYTHING.
It's annoying that you have to create a property for every form you want to reference, but from what I've seen in other engines (namely Unity) that's the norm.