Cool idea GunDoc.
Joachim, basically, you can't just slap a handle riser on a bow that would otherwise bend through the middle and expect it to stay without doing a little more to MAKE it stay.
First, like with board staves and what Eric is doing, you don't need to leave MUCH extra thickness under the handle block, but you really need some. His trick of adding thinner individual lams seems to work pretty well, too. The thickness adds up fast.
Example: I see lots of young guys here and elsewhere trying to make a board bow. They cut out (or intend to) a red oak pyramid bow, 2' wide with a narrrowed handle from their 3/4" thick board. They are intimidated by all the scraping and unsure of their skills, though, so they get someone with a tablesaw or planer to thin the whole thing to 1/2" or less to get closer to intended draw weight. See? Now of course, the handle is both thinner and narrower than the limbs and it would break there, and absolutely will bend more than anyplace else on the bow. So, they glue on a waste piece for a handle. But, the leverages at that too thin, too narrow spot are MIGHTY strong, and it's a total crapshoot whether that glued-on handle piece will work, especially if the fades are not perfect.
So, in this case they need to leave the board 3/4" thick under the handle, thin the limbs to 1/2", then glue on the block and plan on establishing fadeouts. As in Eric's case, sometimes using those thinner slats will work. Sometimes I have to thin the limb further, glue on the handle, then pike the limb and make a recurve. If I can't narrow it and it flexes at the handle, I make a soft handle of cork or layers of leather that will fill it out, but flex (not a good option for narrowed AND thin).
With a crowned stave like you have there, I HAVE had success using a TIED on handle or stack of laminates, even if the handle is narrowed and thin. You have to run this up onto the limb past the flares and tie it tightly so it acts like a fadeout. This worked for me on bamboo bows made of slats. On very LIGHT board bows, I have used dowels to pin the handle on, but run them through the strongest parts at an angle, or they will pop off anyway. Back to front like this \\ //, not at 90 degrees. And, I wouldn't trust this on hunting bows.