Once your keel is completed, there would be nothing stopping you from doing so. I would only suggest NOT to glue all the frames in place then try and install the keel as this would be almost impossible. To install a few frames at the bow and stern then fill in as you go is the optimum method. You will need also to find a way of turning the complete jig/keel assembly around in order to drop the frames into place.
I have not started this yet mainly because I have been building the frames in numerical order so it would not be feasible to start permanently mounting frames yet.
When I do start gluing I will be using pva glue, it has the strength and is much easier to use and clean up.