Still not a legitimate task. Trying to bamboozle the "client" by using a reading off a hobbs meter, rather than using a watch? Thinking outside the box--garbage. You can't do the work yourself, or you wouldn't have asked such a stupid question. You aren't legitimate, else you would have answered the questions posed to you. You continue to hide the reason for the switch; you have no good or legitimate reason for doing what you do.
You're not qualified to do the work. Likely if you ask any legitimate mechanic to do the work, he or she will properly refuse (you can always find someone as beneath board and deceitful as yourself to do the work, however). As has been heretofore pointed out, do the work yourself, and you invalidate the airworthiness of your aircraft.
You lied about the FSDO; clearly flame bait, outright lie, or just an idiot.
If you're renting this aircraft and playing with the hobbs, chances are that whatever you're up to isn't above board, and that applies regardless of weather you're the person renting it to someone else, or weather you're the one receiving it.
Hobbs meters work based on a number of types of switches, ranging from oil pressure to aerodynamic pressure to weight on wheels, gear position, etc. You cannot alter or add to the electrical system without appropriate authority, and executing the appropriate approval documentation...and you don't know what that is or what must be done...you're nosing around trying to get information from folks who do, and refusing to state your purpose or show that you're anything more than either a criminal or an idiot.
So far, you appear to be both.