Can a person that was convicted of a bomb hoax have his federal criminal record expunged

Sorry, but almost never, so in reality, no. Rarely, a pardon is granted by the President. See: http://www.usdoj.gov/pardon/ to learn of how the procedure works.

I've done a little more research into your question, and suggest you look at this article: http://en.wikipedia.org/wiki/Second_Chance_Act , which details new federal bills that might provide some relief for "a person" convicted of a bomb hoax. But a bomb hoax is more than likely a violent crime, and might prevent "a person" from being considered for either the 're-entry' or the expungement provisions of the new acts. But as always, only an experienced attorney, who has been provided with all the facts can give you an opinion on whether you and the new federal acts are a good match.