This is my idea of a great idea as I use the bags frequently and very seldom have any concern for security. When I do, I simply remove the key/caps. I used JB Weld and the caps from Bragg's Apple Cider Vinegar bottles. They're a perfect size and have a textured top that matches the top of the bags and also have serrations on the side that provide a secure grip when turning them. It is essential that the key be centered, cut to the correct length and perpendicular to the top of the cap. This is what I jury rigged to accomplish the task:
I also have a Givi top box that I use occasionally. I did the same with its key. I simply used a smaller black plastic cap that looks the same as the two I used for the bags. I really appreciate the convenience of using all three storage units without digging for a key. On rare occasions when I want the locks to be locks I simply put the key/caps in my pocket or in one of the bags and all is secure.