ipcat

I'd image they'd just block access to anyone connecting from a Datacenter/Cloud Provider, using a dataset like this one https://github.com/client9/ipcat. I'm sure there are more complete paid for datasets out there - probably from someone like https://www.maxmind.com. That would likely block 95% or more of the VPN/proxies out there. It will probably be a bit of a whack a mole approach to the get the rest but you'll get pretty fed up signing up to some obscure and possibly slow/expensive vpn provider to find it blocked 2 days later. What's actually interesting is that they are now openly admitting that they have been turning a blind eye to this before when 1. it's relatively simple and 2. it has always been a requirement of the content rights holders.