Although not strictly relevant to the pitch, I am aware that this is where the sven boffins are.

If you wanted to force 2 cards - could you use a Svengali deck? top-half of the deck one selection, bottom half the other card - would that work in anyone's opinion?

That would work but why go though all the trouble of making up such a Svengali deck.It's easy to force two cards from a regular deck.There are DVDs and books out just for forcing a card.