There is a new crossbow de****er hitting the market in July. It fits most crossbows. It is an accessory that straps to your buttstock. It has a ADF dummy bolt that fools the ADF device. Just strap it on, snap the clips on the string, pull back the draw rod and fire... all in 30 seconds. Check out the video on youtube, it's not a very clear video because it was taken with an iphone and not intended to be posted, but it will give you the idea.
http://www.youtube.com/watch?v=UgMeGC4sKpA.
To retail for between $89-$99 I believe, and will extend the life of your bow, its string and other components while not discharging a bolt. Sure you can fire an old bolt but this is far safer. It's called "The De****er."