I think Xiaou2 holds the record for the most custom built controllers.
http://www.xiaou2.homestead.com/arcade.html
http://www.xiaou2.homestead.com/files/shifter.jpgMan, this is just frickin BRILLIANT for a 2way shifter
back on topic- building a stick shouldnt be too tough, just time consuming and the need to track down or fabricate what you need.
You need a shaft, probably just steel rod- threaded, hollow, solid? whatever
A Pivot Point in the middle somewhere. Im sure you could get some kinda pivot at McMaster, Home Depot or an AutoZone
Some kinda frame to use to mount the whole thing to the CP, as well as steady the pivot and sensors
Some switches to detect your movement. As long as they're fixed and whatever is at the end of the shaft can successfully actuate them, youre golden
In the end though, I think that if youre looking for a one-off stick, youre gonna be better off with something already assembled and available, due to time and possible costs.