Not possible. You'll need to copy those valuable recordings to a DVD Recorder, VCR, or PC with audio/video capture hardware/software.
Does the HD DVR require an active subscription to veiw recordings? I know my DirecTivo's allow me to watch my old recordings after I unsubscribed them, but I have no experience with the HD equipment. If the HD DVR works like DirecTivos, then he won't need to transfer anything (except as insurance against hardware failure).since then I will have them even if at some point I cancel Direct TV.