I'm pretty sure everything to repair your handle has been suggested, but I'll offer this anyway, just in case.

Remove your handle — both pieces — and use something to temporarily hold the two pieces together: superglue or whatever. Then cut a slot that spans the break into the back of the handle with a dremel grinding disc or something similar. I'd say probably four inches or so of groove. Get a metal rod and cut it to fit in that groove. Then epoxy the rod into the groove, holding the two pieces together.

That should dramatically increase the surface area of the contact surfaces for the glue to adhere to, and as long as that's enough to keep that rod/spline from coming out, and the rod itself is strong enough not to break, that ought to work.