Prevent repositional glue from sticking?
One thing that might work to reduce but not prevent sticking is sticker backing paper (waxed/plasticised). Unfortunately it's rather obvious, and not easy to attach because it's designed not to stick to glue.

Another hard to attach (I suggest staples) material is reusable non-stick cooking liner.  It's normally brown similar to much packaging cardboard, but can sometimes be found in black.  This again won't completely prevent sticking, but will make removal much easier.

These won't damage the sticky layer on the card, while one thing that probably would is wiping a very thin layer of oil/cooking spray/silicone furniture polish over spray lacquer.  This approach has the advantage of being applied like a coating, but could end up messy as well as spoiling the glue