in iOS 7, how can I easily specify an email address to be used for FaceTime?
Unfortunately, there seems to be no easy solution to replace the iOS 6 functionality. 

The simplest workaround seems to be to create multiple contacts for each point of contact you wish to differentiate.

Another possible workaround would be to add the different identifiers to 'favorites'. However, these will appear identical in favorites---same name &amp; pic---so it would be difficult to differentiate.

(Based on personal experience and this related apple support thread)