FWIW, I did this for 2.5 years while dating my now wife. As long as i had proof that I would only be in the country for less then 90 days and always told them I was working for an American company and that my American company was consulting for American clients, they were ok with it. Traveling with a recent bank statement also helped to show i had enough funds to cover my stay even if I was on "vacation"

I basically had my mornings free every day until I ate lunch then i would sit down and start work for the day.