Steven Seagal would have a hard time in an elevator because he wouldnt have a glass window to throw somebody through.
In Willy Wonka's elevator he would kick ass though.
Seriously though. I once had a minor altercation with a drunken judoka in an elevator. He was somebody I new and generally could get along with. He got a bit belligerent and tried to get me in a head lock. I was able to get hold of his wrist and apply kote gaeshi. It worked.
I guess atemi, getting a lock in, getting somebody down and then generally sitting on him untill the doors open so you can make a break is the best way to go. The most Aikido I could get out of it anyway.
Personally I have found that when someone manages to get you in an effective headlock it can only be released if one grabs the testicles of ones assailant and twists violently........