DC, Here is one way that worked for me when I just needed a bit more length.
I either mill a handle block to a deflexed angle or glue up several 1/4" or 3/8" lams of the same wood into a deflexed curve. ))), like that. Add your core, or do your butt-splicing like Marc showed. Power-lam if you plan on it.
The backing can then be glued on with a gap of up to several inches (@ 4" was my biggest), between them depending on how deflexed the whole thing is. You grind the front flat which tapers down the backings just at the tips. Then slap a couple of front overlays on to round out the handle.
If the backing has it's full thickness well inboard of where the fade-outs end, you'll be fine. It's held by several well glued down inches AND sandwiched by the overlays, and supported by the powerlam.
It's worked for about 6 bows for me, so far.