Make him work for his food
Instead of putting the food in a bowl, use it for training. Take the food and put it in your pocket. (preferably in a bag.) You can use each individual kibble as a reward, or use multiple for the reward. The cool thing about doing this is it slows your dog down and you can get a ton of repetition in of the things you need to practice.
Make him search out his food
A fun way to feed your dog is to hide the food in different spots. By hiding it in different areas, it's going to slow down how fast he consumes it. Check out the video to see how I teach this!
They make special bowls that have different nodules in them that make your dog fish the food out from within. This causes dogs to slow down as well. Other options are to use muffin tins. Put the kibble in the different muffin spots and then put a tennis ball on top of that. The dog has to move the ball to get the food.
Use a toy designed to slow him down
There are plenty of awesome toys to choose from that will help. These are considered to be "interactive toys." The dog has to manipulate the toy into paying him his food. Check out the video below that shows my dog using his favorite toy, the Monster Ball made by Jolly Pets.