For me the PFC sensor reading under the ETC menu is where I'd start but he's using F-Con for which I have no idea how to use, whether there is a CAMP display etc. Surely there has to be a way for him to retrieve that sort of info electronically; if the PFC which is cheaper does this why not the HKS.
Your solution is by far the most accurate way of diagnosing the TPS but from what I gather these past few pages, it might be a bit too technical for him to attempt by himself and for some reason he won't take the car to a workshop. It's like talking to someone on the phone while trying to guess the color of their underwear - pure guessing game.