Distinguishing Spoken Speech from Played-back Recording of Speech
Do any general-purpose techniques exist to distinguish live spoken
  speech from played-back speech samples?


No, at least not how I understand your definition. 

Consider the case of  "live speech" : some one talks into the microphone, you digitize the signal and analyze it. You can also store the digitized speech and analyze it a day later. Now the exact same samples constitute "play back". Since the samples are identical, you can't distinguish them from "live speech".