I've developed a tool called SpriteHelper that lets you create custom polygon shapes for Box2D physic library. It also select your sprite's UV automatically and gives you copy/paste ready code for Box2D and Cocos2D library.
From the saved file you can load in your project all your texture coordinates and all your polygons for Box2D.
Information in the saved file:
Image file used for the sprites in the scene Image file dimension Image path
Sprite name Sprite UV (top left bottom right) Box2D Polygon vertices
And many more....
Check out the tutorial on the YouTube video posted here: