How to secure screw on filleted curved surface

Hello, I have an object with filleted curved surface at the bottom. I want to attach it to another object above it (on the surface labelled A). I want to join the two objects using screw. The problem is that as the screw head and the nut are larger than the hole, how do I fit/hide a screw head or the nut at B? Any suggestion with photo for easy understanding is appreciated. Thank you.

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