They might function sort of like a figure-8 but a true figure-8 has pretty much perfect nulls 180° off axis which a pair of cardioids won't have.
If you record with just the two cardioid mics in X-Y you can process it to get similar control as you do with a M-S setup. Make a copy of the track, invert the polarity then swap the left and right channels. With the original and copy at equal volume it's like using the side mic only, then as you pull the copied track down it's like bringing the mid mic up.