Apple went above and beyond the normal process, including law enforcment involvement, for recovering one of their prototypes. Why not just do the same to smite the practice and make an example out of those involved?
That, and if they're good at it, bind the ticket to a nontransferable item that has some worth to it(e.g. a non prepaid credit card that was used to purchase it) as well as whatever ID is already required to enter(such as government issue). $1600 admission definitely can demand such protection from scalping.
If Apple has to be draconian about something, nontransferabilty of WWDC admission would be a good place to start. Go Gallagher on the scalpers until they stop.