I've had a play around using 8 playing cards and turning 2 aces face up and placing them 4th from top and at the bottom. For ease, I'll refer to the 2 halves as the 2 aces.
The trick is just to keep tabs on where the aces are.
They start 4th from top and 8th from top (bottom).
The thing is, the spec doesn't know what you're going to do with the cards until they choose a number, so they choose a card and then you tell them what to do.
If the spec chooses 1 or 8, you could simply say that you want a number between 1 and 8.
If they choose 3, do as per the video.
If they choose 4, tell them to count the cards one at a time from the top into a pile on the table, then to pick these up and place them back on top. You're done - one ace on top and one ace on bottom, which is what you're trying to achieve.
If they choose 5, tell them to count the cards from the top into 2 piles. One pile will have 2 cards in, the other will have 3. The pile with 2 cards in will have the ace on top - tell them to pick up the pile with 3 cards first, then pick the pile up with 2 cards in and put that on top and to put all of this on top of the other cards - you're done, ace on top and bottom.
If they choose 6, tell them to count 3 piles of 2, noting which pile has the ace in and make sure they put that pile on top.
I haven't really come up with anything for 2 or 7 ...... crack on lol