I like that idea, but add the roughing spray to it and you can still do spreads, something a standard Svengali can't do. It's the concept behind the Mirage deck. That would make for a sweet color change deck. Thing is, though, you want to do it right, you need precision cutting materials, including a card rounder. Trimming a NARROW strip from the top (or one side!) without a rounder (which is a bloody expensive limited-use tool) could give you a deck you can get away with in most audiences, but the problem is that the more narrow you trim it, the easier it is to fool the spectators but the harder it is to use the deck unless you have a very delicate touch - cutting it that narrow would practically demand using roughing spray to keep the cards together that you want kept together.