At a previous job in the early 90s, when UA domestic upgrades were $25 for 1000 miles, I would put down $24.95 for dinner on my outbound evening flights to a research sponsor's site (we needed a receipt at $25). My logic was that UA fed me a meal I would actually eat in F as opposed to some stupid snack in Y (heh, those were the days), so I wasn't paying for the bigger seat, I was paying for dinner. If I was flying to/from SFO, I'd still only put down $24.95, since every little bit helps.

I very rarely do obvious mattress runs on a business trip, it's just not worth the hassle. What I do about six times a year, however, is a night at the airport hotel at my destination on arrival and then two nights at the hotel "closer" to my client's office. I've never been questioned about that, but I have a reputation in my smallish (230 employee, about 60 travel heavily) company about being very good about saving the company money while maintaining good travel standards.