Thank you, everybody! I got it. I don't think it's a very kind policy, but love is love and business is business. Being on the Wind Star is worth either option: paying too much or the hassle of signing for each drink.
Later: I finally understand why you all have been sending me such harsh answers. I assumed there was a limit to the daily beverage plan, e.g, $100 a day. So, if you had paid that, you paid it, and it shouldn't matter who drank it. I now realize that there isn't a limit, so of course two people can't share a package: that would be two people drinking for the price of one, and totally unfair to WS.
Also, I did just read a recent announcement that both cabin mates do NOT have to have the beverage package. Don't ask me where I saw it, but I did.