Spoiler alert . . . Hm. I might have "cheated" on this. I haven't tried to imagine the actual 2D->3D transformations but instead looked for clues in the 2D images. It's a bit hard to describe - transforming the cutouts in my head so that they match (or obviously differ) in 2D while still giving the same cube. Did not submit though, since I got tired after the 4th set.
We have designed this test in response to that flaw so that when it comes to the harder items it is much more difficult to do so than to use the intended mental transformation and rotation techniques.