If you have HBO at home then I would say that you are within your rights to view shows however you like, but I'm no lawyer.
I haven't downloaded any movies through Bittorrent since the Cease&Desist that Mediacom sent. They graciously allowed me to delete the "offending" content and avoid a lawsuit. It was probably a bluff, but still embarrassing to get caught with my pants down. I strongly suspect if I argued that "I already owned the content from another source" they would print out a copy of the Millennium Copyright Act and ask me to find the line where "ownership in alternative form" is legal. I agree with your reasoning 100%. I just don't think that's the law.
Just move the video files out of bittorrent after they've downloaded so that you stop sharing them with others.
I didn't go to law school, but I think there's a name for this. Something like "acknowledgement of guilt" or "bad-faith avoidance of detection." In the day and age of hi-tech computer forensics (i.e., "cyberpolice"), downloading files and moving them out of your share folder is tantamount to admitting you shouldn't possess them. Again, I agree with your strategy 100%. But it means what it means, and putting lipstick on it doesn't change that.
As I recall, we're not even supposed to be discussing this on droidforums. Hope I don't get banned!