That's one way. Luis von Ahn solved this problem cleverly.
His ESP game has a bunch of images, and you and a partner have to come up with the same tag for each image. Do it fast, score lots of points.
Instead of having people play realtime, he recorded each session, so that if no one's playing that particular image, you're still playing against a human, time-shifted.
Obviously this isn't an exact corollary to Chess (what would the ESP game be, a 1-move chess game?), but there are ways of denecessitating simultaneity.
His ESP game has a bunch of images, and you and a partner have to come up with the same tag for each image. Do it fast, score lots of points.
Instead of having people play realtime, he recorded each session, so that if no one's playing that particular image, you're still playing against a human, time-shifted.
Obviously this isn't an exact corollary to Chess (what would the ESP game be, a 1-move chess game?), but there are ways of denecessitating simultaneity.