Because unfortunately that is impossible. You have the case at the bottom, then the system board mounts upside-down into it, with the USB port, camera, etc facing into the plastic casing. You have to remove the system board from the casing in order to access the USB port and the empty space underneath.

Even if you considered filling up that space with epoxy, you need to be careful not to cover up the hole for the LCD screw, while building it up high enough to reach the USB port. And epoxy dries up extremely fast, becoming brittle if you try to remould it. But once it cures, usually within 24h, it can be sanded down as reshaped that way.

If someone can come up with a way to do it though, I'd like to hear it.