how about saw chip between them?
The more involved way, which can stack two or THREE wedges means bore-cuts. First through the face from the front (personal preference), and from the rear, one below and optionally one above the first, parallel, 1/2" or less spacing of wood between them (puts wood between plastic, creating a slot).
Willie has an interesting way that I never saw or heard of. Maybe he'll put up the pic, if he reads this. It a criss-cross way of stacking using a buncha wedges, 4 might work, but he had 6 or more, IIRC. Intentionally, they aren't run in a stack, parallel to one another.