I think you answered your own question Paragraphs 6 & 7 are pretty clear that BA American Express
account holder must travel on the companion voucher booking.

It's been a while since I last used a voucher, but you are able to choose your 'companion'. It either
automatically adds you or assumes that the account holder will travel as, well, you have too

I don't see how you can use the companion voucher without actually travelling yourself.

H