Ok, I've dug up the documents I had sent.
As of last summer (2024), the options for the payment account owner to identify themselves as being based in (or being sufficiently related to) the geography of the business (the US in this case) and as the person that is, ultimately, authorised to submit a W8BEN (through the same screens for this whole verification) on behalf of the UBO of the business are (exactly as listed by Google):
Driver's licence
Passport
Taxpayer Certificate
Other Government ID
plus a "Reasonable Written Explanation" (with the previously mentioned evidence) as to how this person is involved in the business.︀
In other words, unless you want to have fun with forgery, I'd wager you need︁ a US national (based anywhere?) or a non-US national based in the US.