soak the stem in an ethanolic solution of vardenafil, tadalafil, or sildenafil. The last one is no longer under patent protection and should be available cheaply. Repeated application may be necessary. Call a metallurgist if nothing happens within 4 hours.

Also, why do you need a stiff stem? You are a pursuitist/endurance trackie, no ?

seriously though, clamping area? A Profile Design Aris might be good, and it's available as a -25 stem.