[mothered]

458 grams.

It's almost half a kilo, so too heavy for the missing Item method.

What method should I use then? I think my post office will want me to sign it. Not sure exactly.
Order some kind of liquid with it? Alcohol? And say it spilled and I can't return it because it is very flamable?

A signature on receipt of the package, Is only relative to the DNA method.

You can certainly do what you've mentioned above or alternatively, use the wrong Item received method.