How can I overpower a dead keyer (someone keying over top of me purposely)

The legal way. Try to nail down his location - get together a couple of friends and use normal locating technique, see it as a fox hunt exercise. Of course - it takes some effort, and when you have his address call in the FCC.

One of you have to be the decoy though...

 

I suggest quietly locating him and then file a complaint. If you hand him to the fcc on a silver platter, they will definately be interested- most of the work is done. Once they catch him in the act, it ain't gonna be pretty. Take a look at the 4 most recent-
http://transition.fcc.gov/eb/AmateurActions/Welcome.html