If Ricks solutions don't do the trick, you could use a dremel tool with a small wire brush to remove most of the old glue.
If it's a break through the wrist running with the grain, removing a small bit of wood with the old glue won't hurt either,,, just don't remove any wood near the edges. I've used dental picks to remove old glue as well, but it's a slow process but should work around the edges.
Clean up the old glue well enough until you can press the stock pieces together so that the crack lines fit together tightly, then re-glue it together.
I've done some practice pieces and one gun using Gorilla glue and the stuff seems to be really strong. It also foams a bit when setting up and will fill in any internal void areas. Wipe the foaming goo off the external surfaces with a damp lint-free cloth before it sets up.
You can also add a drop or two of a water based stain to the glue before applying to help match the surface color on the stock.
John
