Ah, didn't see that part. As the holder of a JAA/EASA commercial license you'll have to get a FAA private certificate first (either one "based on" your JAA/EASA license or a "stand alone" one. Then you'll have to turn right around and get a FAA commercial. There's no provision to "convert" a foreign license to a FAA certificate at a level higher than private unless it's Canadian and unlike the ATP, there is no relief from having to hold a FAA private certificate before you apply for the commercial unless you have military flight time.