OPTIONS processing

In my setup I use * as a PBX hooked up to Broadvoice for dialing outside. When * registers with Broadvoice, it keeps sending OPTIONS msg. But the from field has the user as “asterisk” instead of the from_user specified for that registrar. So Broadvoice keeps responding with 404. Is there a way to either stop this message altogether or tell * to use my Broavoice user name?