You can certainly try frozen, if he takes it great. But don't be too disappointed if you don't have success right away. Most of the times when I have a new ball python, I want to make sure they're feeding regularly on a schedule before trying frozen. From the description, it sounded to me like the snake was scared off of feeding by being watched. Since the size of the snake was also described as being the size of the mouse at it's widest part it sounds like a fairly new baby. Because of the time of year, I'm also guessing it's probably a CH import, many of which have never fed at all before being sold. Do you have any more background information on the snake? Did the breeder or importer or pet store say if it was feeding and what it was feeding on? In any case, spix14 is right in saying that you should wait a few days before attempting to feed again.

Mark