Technically there's no reason you can't cut a headstock off and reattach it. Loads of headstocks are glued to the neck with a scarf joint.
If you took two inches off the neck, before you glue the head back on you'd need to get a shorter truss rod, which would mean fretboard off. Once the head is glued back on you'd need to reshape the neck all the way along its length to loose the new 'shoulders', then fit a new fretboard and slot it for your new scale.
Completely feasible, but ultimately pointless.
Edit, I've re-read my post and 'pointless' is the wrong word, especially considering what I'm in the middle of. More an awful lot of work which could go wrong and render the bass unusable, for relatively little gain.