Well. I guess this is a little late for your situation, but this may be helpful for others in the future. The Virtual Weber has good information on holding, storing and reheating cooked foods including how to keep food warm safely for an extended period.
Naturally, it mentions the FTC method, but offers a suggestion for holding food even longer if needed. Offers preheating the cooler with hot water first, but also offers this method:
Wrap several fireplace bricks in heavy duty aluminum foil. Heat in a 500°F oven for 30 minutes. Place a thick layer of dry towels in the bottom of the ice chest, then add the hot bricks, then a thin layer of moist towels. Add foiled meat, then more towels. Close lid.
Using the normal FTC method, a brisket was kept at or above 140*F for 3 hrs and 15 minutes. I would think using the brick method could get you to 5 hrs if needed. My only question would be whether the hot bricks would continue to cook the meat. Maybe place a trivit between the bricks/moist towels and the foiled meat.
The article also covers both hot and cold storage of food. Hope this helps some.