One needs to cheat a bit. There are $48$ missing cards, which can be thought of as $1$ to $48$. (The **meaning** of these numbers depends on the $4$ remaining cards, but Sal knows these.)
Pat and Sal have to encode every integer from $1$ to $48$, using the $4$ cards. There are $24$ permutations of the $4$ cards, not enough. But if Pat is allowed to present the $4$ cards to the magician all faces up or all faces down, there is enough information.