One possible way to clamp the lip while the the glue is curing would be to actually put some small screws into the lip to compress it together. Remove the screws after the glue cures and fill the holes with epoxy or putty.
Actually, if you aren't concerned about astetics, you could use pop rivets (with backing plates) and just leave them in when done.
Also, it might be a good idea to tilt the hull so that the crack is the low point. That way, the glue will pool in the crack and create a fillet rather than just run down into the bottom of the hull.
I would probably wrap some glass around the lip to help hold the deck and hull together.
Last, make sure you check the repair before hitting the water. Rig the boat up and pull on the mainsheet hard. Go to the bow and check the status of the crack.