Yea they open up. But like Ed says some checking occurs at the taper and so the rubber might act double to help stop that. I was intrigued by your clamp idea too.
I had to think back to how I've dealt with stiff handles and I realized that I've only ever done one stiff handle after the handle did the clam thing. I flattened the handle glued on a hunk of hardwood. But I flattened too much and the handle popped off. Shoots just fine without the handle.
Usually the staves are not long enough for a stiff handle, so all I've ever done was use electrical conduit section to glue in billets. I did one molle with a take down handle using two especially wide pieces of OS. I've also filled the clam with epoxy and wrap with leather, and I've done some bendy handles. So, never pursued the checkless stiff handle yet.
I know others have and I think the consensus is to seal the whole stave up really well, for like a year. So I don't know what forces you may be dealing with to allow the limbs to dry faster than the handle.
If you had a stave long enough, and were willing to do a lam handle, you could flatten, kerf, and seal the handle right from the get go and you'd probably get minimum clam effect. Then when it stops moving fill any voids and glue on a handle. Otherwise I think you are on the right track with your rubber and clamps, except that I would remove the bark asap.
And its not so much getting to the pith as it is just reducing the stave so it can dry evenly.
Its amazing stuff. I have a concave belly stave that the string wouldn't align so I abandon it last year. It was at floor tiller or better. Recently I wanted to test the tension strength with the concave belly so I bent one limb over my knee. It went to 45* and took alot to get it to finally break. I folded it completely in half and it stayed together. The break looks like a paint brush with a thousand strands of fiber sticking up.
