One possible modification is to make a stronger suggestion. A classic hypnotic induction is to place someone's hand slightly above and in front of their forehead. Have them stare at a spot on their hand. You suggest that, as their hand slowly moves toward their head, their eyeslids will become heavier and start to close. This is repeated until the hand touches the forehead, at which point the person should be in a light trance. You can see an example on Youtube at:
You can do something similar by modifying the finger-touching routine mentioned in 7 Deceptions. Start out the finger-touching rountine as described in the book. Ask the volunteer to stare at the tip of your finger. As you slowly move your finger towards the volunteer's finger, you can say something like: "Now, as you watch my finger slowly get closer to yours, you can let yourself relax and remember how easy it is to forget things. You can just relax and watch my finger drift closer towards yours. And as you watch my finger, you can notice it becomes easier and easier to forget. The closer my finger gets, the more relaxed you can feel, and the easier it is to forget. Just relax and forget. Relax and forget." While saying this, slow down the rate at which you are speaking and slightly lower your voice, becoming more soothing and relaxing as you go. This should help strengthen the suggestion to forget. When your finger touches the volunteer's finger, pick up on the instructions in 7 Deceptions again.
Also remember the illusion *always* works as far as the audience is concerned. This is because the audience always remembers seeing a different card than what the volunteer remembers seeing.
It helps to set things up with the patter described in 7 Deceptions about the old film. Later, if the volunteer is really insistent on having seen a particular card, you can simply remind him what you said about the old film. This indirectly explains to the audience why the volunteer is so insistent.
I have also modified the illusion by using a color change instead of the card manipulation described in 7 Deceptions. After the volunteer shuffles the cards, stand between the volunteer and the audience. Take the cards and turn to face the audience. Hold the cards in the left hand, card facing the audience, with the right hand covering the bottom card from view. Tell the audience you want them to remember the card they are about to see. Remove your right hand, show the audience the bottom card, then replace your right hand. Now turn around and face the volunteer. When you remove your right hand to show the volunteer the card, perform a color change called the "winter change." (I learned the winter change from Ben Salinas "Hot Shot Color Changes" DVD, available at Penguin naturally.) Keep your hands fairly close to your body to protect visual angles from the audience. Cover the bottom card again and it's done. This handling seems more natural to me since I don't have dexterous fingers.