Alright, first set up a basement in the card shop.
Then set up tables that allow people to play variations of the card game with no effect on score.
Some examples:
3 and 4 ways
First to 0 HP wins
4x4 grid(cards may or may not last longer)
side warp(a card on the left side can be attacked by a card on the right side, vise versa and works the same vertically as well)