DOOD!!! Thanks!! I didn't try the mod, but it lead me to this:
http://www.subsim.com/radioroom/down...do=file&id=717
Just some simple changes in a .cfg file and you can now take control of the outer ring to manually input mast height... ANYTIME!!
I tried it, and sho 'nuff hit a carrier from 2500 yards away!! (fired 6 fish... first one, BIG explosion, 2nd one killed him, 3rd and 4th were just for the fireworks, 5th and 6th went past his bow because he had stopped moving)

So... I can vouch that it works, and it's accurate.
This is EXACTLY what I was looking for. Now I just need a way to make it let me use the Stadimeter anytime I want, not just when I'm looking at a ship.
Thanks for pointing me there, and thanks to muchausen for posting that!!
Off to kill me some Japs...