Schools are looking for evidence of a capacity for independent investigation. This is what you should aim to show throughout the application process. Publications are exactly this: evidence, nothing more or less. Why would they be? Do you think schools make their reputation/funding off of the number of publications that admitted undergrads have?
It sounds like the OP's friend's PI is a nice guy trying to do him/her a favor, but an 'easy' publication may not only be worthless but potentially hurtful. If his PS, recs and interview answers can't present a unified picture of exactly what he did and where this project came from and how it has affected his future plans, then a publication will actually call the credibility of the rest of his application into question. If you think about who your interviewers are you'll see that this can lead to a lot of trouble. These are people who grill grad students, have undergrads in their own labs, review articles for publications, interview scores of other candidates, and have been in his shoes and are aware of the accompanying temptations.
If your friend goes through with this, he'll most likely distract from the competitive aspects of his application by focusing all their attention on a "research experience" that he can't give evidence for. Worst case scenario, he tries to make more of it than it is and gets caught out with major repercussions for his future career. Instead, he should ask his PI if he can actually work on an independent project with him/her. It sounds like he's been lucky enough to find someone willing to support him.