Try this: Fit your handle thickeners, do all the filing and scraping and sanding till you like the size, layout and feel. Then....on the belly side, saw several kerfs back to the original bow, only in the new handle section. I'm guessing here, since i can't see your bow....make the kerfs an inch apart. THEN.....cover the handle area with the leather of your choice , nothing too thick. Now, the bow will still bend in the handle, the short sections will stay put and the leather cover will hide it all and not let the kerfs pinch you.
piper