This goes against the core message of the article. The candidate is supposed to think about a problem on their own, and propose a well-reflected solution on Monday. That's pretty much the opposite of "sit down in this noisy corner in an unknown environment and give us something in two hours".
> The other problem is that when you pay them you generate all sorts of nightmaris legal liabilities.
If hiring a freelancer to do a little thing tends to generate all sorts of nightmarish legal liabilities, your company is either a government contractor or it has even bigger structural problems than hiring.