Piece of cake...if we are "a bit lenient" (cough) about the "dice look"... (hard cough) ...and, additionally, employ, uh, "selective blindness"... (hard persistent cough)
Yes, Jaap Scherphuis already answered that a proper solution is impossible (and, of course, the first thing I did was to upvote his answer; his answer should be the accepted answer). But workarounds are, in this case, kind of easy. First I though of some sort of binary coding...but that's too complicated.
So I chose white, went to some online Rubik's Cube simulator and did five moves:
On top, you see one (1) white square. This is, obviously, the (1) side of your die. The (6) side is, of course, following the "7 rule", on the bottom (not shown).
To the right, you see three (3) white squares. This is, obviously, the (3) side of your die. The (4) side is, of course, following the "7 rule", on the opposite side (not shown).
To the left, you see five (5) white squares. This is, obviously, the (5) side of your die. The (2) side is, of course, ...ah, you guessed it already.
Now, there is, of course, some minor "cosmetic issue". If you happen to look at the (2), (4) or (6) side, you won't see any white pieces (so "x" is unknown). But don't despair. As you happen to know the "7 rule", you can just lift the cube, look at bottom (which will yield value "y"), and, with a bit of math, you can solve the x=7-y equation to yield "x".
Well, technically, you don't need to lift the cube, you can just look at the five exposed sides to determine what's on the bottom.
Important notice: this is meant to be a "fun answer", as it does not meet the "look like a die" criteria. But it might help you if you want to play "Schocken" and lack the proper three dice to do so...but, luckily, find three guys in the pub who happen to carry their Rubik's cube with them all the time.