gyopi,
I love the idea here.
I think what makes it (the one card with half a deck resting on it) appear to not be magic is the bending of that single card. If you were balancing half a deck on the corner of a single card and holding the single card by it's other end, it would bend under the weight of the half-deck. In the video, it does. There's no magic there, just standard Physics. ;-)
But! What if that single card didn't bend during the balance/levitation effect? What if the effect was presented as "this 8 bestows upon the deck a near-weightlessness" such that you put the single card's corner under the deck, holding it from the other end and holding the deck from the far end as well. Then you carefully release your fingers from the deck... the deck doesn't fall with gravity, and the single card doesn't bend under the weight. THAT would look like magic. =) That's how I envision it in my head.
As a bonus, if after that part you put like just one finger under the half-deck to "support" it, and then are able to slide the single card back and forth freely to show that it's not connected... and then immediately let go with the finger under the half-deck and it's floating again... that would be neat.
Best of luck to you!