The last few times I flew, I didn't even get a boarding pass until after I checked in, so this would require leaving the airport (or just having the printer and equipment with you, which seems pointlessly risky). At Philadelphia, we didn't even get boarding passes; they were so far behind and had so many rescheduled flights they just told us to take our IDs to the gates where they printed the boarding pass and scanned it.
I have also never had a boarding pass that wasn't scanned, and every time it has been scanned, they have checked the name on the computer against my ID and then against the pass. It sounds like this isn't a universal thing, though, so I either look suspicious or have flown right around alert times.
One thing you could do is look up the airport online and check what information they have from TSA guidelines, as they usually tell you up-front what to be prepared for in the event of a security check.
In terms of crimes, this is definitely a form of forgery/fraud. Even if they don't charge you with some sort of crime (which is unlikely), TSA will probably take down the flight, gate, and seat #, have the gate pull the information, and revoke your friend's boarding pass when he tries to board.
In short, funny idea that may have worked a few years ago, but now it's probably not worth it.