Andrew Gelman has an interesting point in a blog entry about religious commitment devices, such as a WWJD bracelet. He says that the bracelet is not a treatment, but rather it goes along with a set of behaviors and commitments, and it's a sign of that. This issue of commitment devices applies as well to my virginity pledge work: like the WWJD bracelent, the pledge may not be an intervention, but rather it could be a sign that someone has a certain identity, so the pledge itself isn't important.
Conversely, Gelman's argument could be critiqued on the grounds that there are folks who have the set of attitudes and behaviors, some of whom have the bracelet and others of them who don't, and conceivably, it would be possible to balance the two groups and get a treatment effect. Whether the treatment effect of wearing a WWJD bracelet could possibly be meaningful is a good question.
More thought needed.