sure, you could log anything you want & chances are your gonna get away with it ... unless something like this happens:
There was a guy in florida doing some hour building. Almost everytime he was flying around he saw the same airplane always doing touch & go's (not based on the field though). So he figured since this plane isn't from around here no one is going to notice if he adds some flight time with that tail number. Well, when he got enough hours for his next rating, the examiner inspected the logbook. Guess who's airplane it was? It was the examiners.
Unless something like that happens to you, you should be okay. Though i wouldn't do it. I always keep the receipts as records & if the receipt isn't to clear, i ask the FBO guy to sign the logbook. I don't want some FAA guy taking my expensive hours away 'cause i can't prove them.