The elm and Osage in my bow riser isn't any stronger than it would be in a one piece. In fact, with the brass and steel, I would say it is even stronger.
I do want to clarify something however, because I should have been more specific. I would never suggest this for a bow that is not straight grip hill style! My god, there is a wide variety of longbows out there and a lot of them with riser/grip styles whose integrity would be compromised by a structural modification (this includes wud's recurve!).
My god, I don't know what I was thinking. It did cross my mind that his longbow may not be a straight grip/hill style, but I REALLY should have mentioned it: With the grip style of many bows, this would be a complete disaster, and it was negligence on my part to leave it for anyone reading to decide whether their bow is suitable for modification. I should have been more clear.