You can summon an actor via script call provided that actor is already configured for TBS battle by using the script call:
const x = $gameMap.selectedBattler().x;
const y = $gameMap.selectedBattler().y;
$gameMap.addExtraActor(1, x, y);
This will summon an actor on the current battler location but without any turn limitations as the actor object is currently not returned from this script call to directly add states to it yet.