No, this is not legal. Any respectable employer would give you zero credit for this time, and fire you if they found out about it after the fact (aviation is a small world, don't assume they won't find out).

Any clown can twist and interpret the wording of the regs to his advantage, but the reality of law and regs is a combination of the language and the past interpreation. I can guarantee you that the FAA (and the admin law judges) have not interpreted it the way this guy does.

There is a way to sit in the back and legally log PIC. It applies in 141, 121, and 135 where you have two pilots (or one pilot and one instructor) up front and a check-airman sits in the back (or jumpseat) in order to do a required flight check on the instructor or pilot(s).

But even if it's a 141 school, you would still have to be a 141 certified assistant chief pilot, one of the pilots up front would need to be a 141 CFI, and you could only do this once a year (for each 141 CFI).