I have a violin without a fingerboard. The neck is broken clean in half right below the head.
I can get the two pieces to nest back together and glue them, but I also want to add a splint on the fingerboard side of the neck.
I saw somewhere that if the fingerboard is off, you run elastic cord through the holes in the headstock and around the tail end of the instrument. Tighten as much as you dare, and then you clamp the neck to a flat surface or splint.
I've not taken a whack at it yet. Have to fix a belly crack first. Also, I think I'll varnish the instrument and head first and then glue the neck together, and then put the fingerboard on right away. I'd feel leery to have glued up the neck and then screw around with it while finishing and sanding without a fingerboard to hold it together. Plus the neck is not traditionally finished anyway.