they could deploy anubi
The Free Software Foundation's position (from the linked-to article)...
"Anubis makes the website send out a free JavaScript program that acts like malware. A website using Anubis will respond to a request for a webpage with a free JavaScript program and not the page that was requested. If you run the JavaScript program sent through Anubis, it will do some useless computations on random numbers and keep one CPU entirely busy. It could take less than a second or over a minute. When it is done, it sends the computation results back to the website. The website will verify that the useless computation was done by looking at the results and only then give access to the originally requested page.
"At the FSF, we do not support this scheme because it conflicts with the principles of software freedom. The Anubis JavaScript program's calculations are the same kind of calculations done by crypto-currency mining programs. A program which does calculations that a user does not want done is a form of malware. Proprietary software is often malware, and people often run it not because they want to, but because they have been pressured into it. If we made our website use Anubis, we would be pressuring users into running malware. Even though it is free software, it is part of a scheme that is far too similar to proprietary software to be acceptable. We want users to control their own computing and to have autonomy, independence, and freedom. With your support, we can continue to put these principles into practice."