i dont think so since you only have one camera in Stencyl.
if the game is extremely simple, you could fake it if it would be like an endless runner kind of game.
in theory what you would be doing is moving everything on your "screen" execpt yourself, and same goes for the bottom "screen", you would be moving everything but the player 2 actor.
but i will give it a fair 1% change it would be doable.