Qwik-Sane?

Anybody else remember this silly old sliding-block puzzle from Wff’N Proof?

Anybody ever solve it?

Would you be willing to post the solution in a spoiler box?

(I think it isn’t possible, but I’m not sure. It might involve some sort of “cheat,” like “slide the cube into the third dimension,” or whatnot. Or maybe I’m a dolt…)