Like Pat says, or I use a short Z splice on belly lams and the glue a thin riser/grip section over the join.
A short Z is very much easier than a long one.
I wouldn't trust a butt joint, although theoretically its fine, there is very little glue area and the shock/vibration of loosing may cause it to crack.
I'm actually working on one now, continuous boo back. Yew core with short Z splice. Ipe belly, with a 3" section in the middle joined to the 2 end pieces with scarf joints (yes, my Ipe was just some off-cuts that weren't quite long enough
) and a thin grip/riser lam over the centre where the scarf joints are.
Del