I had the same problem with my Petrel. In my setup, the hooked stem stayed in the hull and is glassed into the boat. 

I'm not sure this is the best solution, but I spent some time wiggling or banging my forms until they all were loose from the hull. Several came loose with a pop...easier than I thought.  Then I took a screwdriver and wedged it carefully between that long, vertical form and the stem up at the top, and the hull with the stem popped loose from the form without doing any damage.

I had worked up some contingency plans that I didn't resort to. They involved removing those thin bow forms from the vertical piece that's attached to the strongback (which means probably destroying the forms), and then taking a hacksaw blade to separate the wooden stem and hull from the vertical form. I was also thinking of breaking the vertical bow form loose from the strongback and wiggling it from side to side....but I got the whole hull loose before it came to that.

The hull and deck are like eggshells when you get them off. I realized if I dropped anything on them, I might undo months of work. I was a nervous wreck until I got them glassed.

Good luck.

   I seem to recall going in with a fine saber saw blade and sawing off the part of the form blocking the hook from passing. Wasn't planning to use the form again and I would still have worked if I had.

Ed