Funny, I think I was too proud to look up a tip on this subject and came up with a similar solution that worked for me.
I used fishing string around the 3" extenstion's shaft to pull it out after the spark plug was unscrewed completely. also used the universal upstream of the 3" and the longer extension as you did. I then separated the 3" extension and the socket and left the socket inside the hole, along with the sparkplug which was in the rubber insert.
I was then able to use the head of a 10 penny nail to hook the socket from inside the square hole and grab it with my fingers as it got high enough to do so...at least I think that's how I remember doing it.
