The "good way", as you put it, is exactly how engineering interviews work at Google. The person assigned to take the candidate to lunch is completely separate from the actual slate of interviewers, and does not submit written (or any other kind of) feedback into the hiring process.

In my team's case, it's generally the person who did the candidate's phone interview who takes them to lunch when they come on-site, but I don't know if that's a common thing.