Do NOT shave your dog as suggested above.
Do invest in a professional dog dryer. Check Ebay, you can sometimes find them reasonably priced.
Or see if there is a self-groom shop in your area that you can stop by after your dog goes swimming. Just put him on the table and use their dryer.
As suggested above, use a furminator frequently to help thin out his coat and get rid of as much undercoat as possible.
When using a hairdryer, be sure to "back comb" his fur. Brush the fur against the way it lays so you can get down to the skin. Concentrate on small areas and work slowly.
Always use as narrow a nozzle as possible. That will concentrate more airflow in one spot.
Some vacuums/shop vacs have a reverse setting. Basically set it to blow instead of suck and use that to dry him. Again, try to use a narrow nozzle for more pressure.
Drive him home with all the car windows rolled up and the heater set on high and blowing right on him. It will be incredibly uncomfortable for you but it will help dry him. It's kind of like being in a clothes dryer only without all the tumbling around. :-)