The first kayak I built (High-Capacity Great Auk) I had the same problem with the forms.

I did exactly the same as you (Hot-glued the forms, on the strongback, to the deck shear-line, and then started the deck.

I did not screw the forms to the strong-back, just made sure the spacers were well-tightened with the centre wedges.

When I had about four strips done on each side of the deck, I removed the hull. A sharp tap with a hammer from the inside right next to the form broke the hull free from the form without damage.

One mistake I did make was fibreglassing the outside of the hull, then leaving it off the forms for a month or so - DON'T do this!