If there was an option for a family account, you could probably structure that a couple of ways—say one family account pays for five accounts, you give the original payer four unique “lifetime for free” or “year for free” or whatever coupons via email and register four more members under four different email accounts with those coupons as payment, creating five unique accounts or extending pre-existing accounts. Like you point out, you couldn’t really control whether the “family” members are indeed family without some extra accountability system (I bet professors out there would leap on something like this if they could get the funding, and someone could post extra codes on the internet to strangers, or apply extra coupons to their own account), but you’ve at least satisfied the “unique accounts” requirement. Anyway, it’s up to WK whether they want to offer such an option and how strict they’d want to be with it.
The problem I can see could be people registering for multiple accounts and then jumping to another account when they get banned, but that’s some premeditated money and effort and hassle. Unlikely.