i had an idea that if you riffled through the cards and let the spectator pick a card that's not the force card. you then say "i knew you would pick that card because all of the other cards are the same" and you riffle showing all of the force cards. ofcourse you can't use it in the same show as the original svengali deck because it would give the ending away, but you can try to use this effect as a small side trick or you can make the effect longer with more patter.
No disrespect, but wouldn't a rigged deck and any basic force do the same thing? as a lame side trick, I always show them the deck is well shuffled, then force the card, then tell them to make sure there card is in there, then show them all the same card. It's nothing fancy, but it works well for kids.