They perform a sting operation, simply downloading the content from you (much as undercover cops would buy a bag of weed)...

Once they establish the precedents with Napster that any "space-shifting" is presumed copyright infringement (and that is a precedent they seem to want quite badly), they will then apply that precedent (any any others set in Napster) to the prosecution of identified sharers...
(Such is the problem with being identifiable)...