The best advice is to get a local attorney, they usually know people in the court house who can get these things done in a timely manner.
If you can't, then you go on Sept 7th and explain the situation to the judge. Provide a copy of the letter as well asking for a postponement. They may not grant the postponement until January, but may work on a payment plan for him and most likely will not issue an arrest warrant. An arrest warrant is usually only issued if the traffic violation was serious enough(DUI, etc) or for failure to appear. You showing up and explaining the failure to appear will usually be sufficient to quash any arrest warrant.
Again, the best bet is to hire a local attorney to fix the problem.
He won't be discharged over a traffic violation unless it is a MAJOR violation, such as a death. He is not being discharged for going 70 in a 45.