Sticking explosives up there would be expected from the one off type terrorist, but for any planned operation like 911 they would probably get surgeons to implant the device internally. Remove a kidney if you need room, add a lapband, give them a couple weeks to recouperate, and you're in action.

Then Rapiscan would have a news release saying they have a update to increase the power of the x-rays to locate "hidden" objects.