How do I deauthorize a computer that is no longer in my possession?

I have reached my authorization limit and now have a new computer. My library and playlists were transferred prior to selling my old system, but I did not deauthorize my old system prior to selling it. The new owner has wiped the computer and does not subscribe to iTunes. There are no other systems on my list that are accessible for me to deauthorize. I would like to authorize my new computer but cannot until Im able go through the deauthorization process for at least one of my prior computers. There is no topic in the help community that specifically speaks to this scenario. Anyone out there who can help me sort this out? Very much appreciated. Thank you.