I'm on a kick lately about infusing CHOICE into my magic presentations and structure. Sometimes the choice requires no change in handling, such as "What four-of-a-kind shall we use?" or "Should I find the red or black Queens first?". Other times, it my require two alternate endings. I'm working on a triple card to pocket routine now. For the last card, I'm working out a way to ask if they'd like their card to melt from the inside of my pocket to the outside OR from the outside in. Of course, I'll be prepared either way, and depending on what they say, they'll never see the alternate ending.
This train of thought has me thinking about every effect in my repertoire, looking for opportunities to add choice. Why do I think this is important? I think it's a great way to: 1) Engage my audience in the experience; 2) Let them play a genuine role in where the magic takes us; 3) Shift the experience from being predetermined to "in the now;" and 4) Raise the perceived impossibility by being able to deliver on their choice.
Give it a try. I'm curious to see what you come up with.