Most card cases are about 1/16 of an inch / 2 mm taller than the height of the cards they contain. On the front side of the card case opposite the back flap side, two stops are positioned, one on either side of the indention under the sticker sealing the case when purchased.

To make this up, place the cards in the case and with a fine pencil draw a line across the inside of the case along the top of the cards.

Measure the width between the side of the case and beginning of the center indention. For a poker size deck this is about 3/4 of an inch / 2 cm wide. Cut two strips of stiff cardboard to that width and about 1-1/2 inches / 4 cm long. The cardboard must be the thickness of one playing card. I used a sheet of index card stock / cover stock sold by stationers, but pieces cut from an old card case will also do. A rectangle of playing card stock could be used, but the finish on it makes it difficult to paste down.

Apply paper paste to one side of one end of the paper rectangles and position the ends inside of the case so they meet the pencil line. When the paste is dry, trim off the portions of the rectangles extending out of the card case.

Handling

Left, the single card held back in the case.
Right, turning the case over frees the card so it is loose in the case.

Place the deck in the case and close the case. Pick up the case flap side up. Pull out the flap with the opposite hand. Revolve the hand holding the case so the flap is up. Hold the opposite hand palm up near the case.

Tilt the case down, not quite upside down, but at an angle, and let the cards slide out of the case to be caught by the open hand. Place the card case, flap side up, on the table.