Factory Restore of 4.** Firmware

I've got two ATV2's running a 4.* firmware as I  much prefer the horizontal layout of that firmware versus the newer firmware. Given Netflix has stopped working on that firmware I am thinking about selling one of them. Is it possible to do a factory reset without the original firmware? I wanted to keep it on the lower firmware pre-sale as someone else may like that version. I am thinking that I might try a FireTV with the Plex app as Plex works very well with my server. Heretofore the jailbroken ATV2 was the best instant on device for me.