Its an idea, though id still be concerned as you've got a limited material around the rear of the heel once the neck is in there. Hard to tell from the photos but that section doesn't look much thicker than 3/8" or so. I guess its one of those things that you aren't going to know unless you actually make it happen.
You might also strike issues with the corners of the pocket, if you try and take your graduated heel shaping too far.
The dowel idea has some merit, but you will need to be absolutely spot on with your drilling and placement. It would be an interesting (and nervewracking) exercise.