Use CharacterSetOnStage or whatever it is on a player. Set it to 0 and then set it back to 1 in the next line of code. It's unnoticable by the player, and seems to activate the trigger.
Well my player seems to flicker when I do this

It's also not activating the trigger.
That's strange, it seemed to work for me and I definitely had no flickering.
Honestly, while it's a potential bug it can probably be worked around because how often is the player going to be just standing still? You can pause any timers while the player is in dialog to prevent the switch from happening then, and it should go largely unnoticed.