Nestor's only a half hour, I'd consider that a short too. There's that, Signal 30, Santa, Act Your Age... still not enough to fill a disc.
But what about all the other odds and ends that RiffTrax has done? The "Mike's first weeks", the Chad Vader special, the disturbing Holiday Havoc thing, the Departed riffs, the campaign commercials, CGI Mike, the trailers, etc etc. Or maybe some of the comic con footage that's come out.
If only we had a better source than YouTube for some of those.