I like the mortice & biscuit idea but I would first want to get the cracks on each side filled & closed up a much as possible. I still like the original Acraglas for something like this but others may have ideas on the proper adhesive. Whatever you use needs to get into the clean & deoiled cracks & the cracks pulled tight as possible w/surgical tubing.
After curing then cut the mortice under the trigger guard. A vertical mill or drill press w/ compound table + appropriate cutters would be the best for cutting the mortice. Assuming you don't have either you could drill holes to the approximate width & depth of the biscuit & clean it up w/chisels & a bottoming scraper to fit the biscuit. I would probably use Acraglas to secure the biscuit as well.
Done properly it should be nearly invisible & very stable.
