I'm not trying to use flexibility to defend against an Americana. I'm trying to prevent an injury from someone who applies an Americana and would reasonably expect at least a few more inches of travel from doing serious damage unintentionally. I assume most people here when applying a submission would first, apply the appropriate grip (Americana, Kimora, rear naked, etc) then, slowly apply pressure until they get the tap. For this particular submission on my shoulder, applying the grip would be akin to normal person's having their elbow dragged down towards their belt and yanked several inches off of the floor.
For example, I was working with someone on attacks from kesa and showed them the Americana lock where you place the opponent's wrist under your calf with his arm bent about 90 degrees then lift your hips. I could not have my wrist placed under his leg, that's how inflexible I am.
I'm a 48 year old tall skinny white boy with long floppy arms like a gibbon. All I want to do is increase shoulder flexibility so I don't get hurt unintentionally. That's it.
Thanks for the suggestions and links. I'll give those a try and see how they do.