If you were given a specific list of accounts to bulk mail, then possibly your boss has already ensured his account is not present. Why not try making his address known to other spammers, perhaps by posting it to a newsgroup or signing up for some iffy free services? If you do this at only a moderate rate, it is less likely to arouse suspicion.

To reinforce what has been said before, creating a throw-away anonymous account (Hotmail, Yahoo, etc.), sending the spam that way, then reporting it seems to be quite an ingenious approach.

Above all, however, I would suggest resigning from this ethically-questionable job.