Is there a way to empty my hands?
There's no way to empty your hands, you just have to select something else from the radial menu.
This seems a bit of a design oversight, but it only lasts a level or so before you pick up the revolver and that becomes the default thing in your hands.
It's annoying, but I suspect that they didn't bother with a 'deselect' mechanic because players would only need it for about a level or so, meaning that it would only add confusion.
If you load your last save, then you'll resume with nothing in your hands. So find a save point, save, then load current save. Voila, empty hands.