What you are describing is very very close to padding your logbook with fraudulent time, and if discovered the FAA could potentially yank your certificates. They have come down hard on folks who where logging "dual received" and "dual given" without any instruction taking place, and taxiing around just to run the hourmeter is also fraudulent.
I remember a story a CFI friend once told me, about foreign students from a hot dusty country who where here just too build time to meet a requirement back home. They would rent aircraft and fly around building hours. Well, one day he gets a call from an FBO of a nearby airport, who says, "did you know you had an aircraft sitting here on the tie-down idling?"
Turns out these guys where flying to an airport 20 miles away, tying the aircraft down and leaving it running, then going to hang out at the restaurant.