Get a crippled bird in your hand and throw it like a "fun bumper", meaning dog doesn't have to be steady just needs to have fun. If the dog gets to the bird n wont pick it up jog out there saying good dog in an excited voice scoop the bird up and toss it 10 feet or so, I like to quack or make what ever sound gets the dog excited when throwing. When he picks it up, give lots of praise and do it again. Keep it exciting.
I would try this before using pressure and making it an even bigger deal for the dog. You never know it could work within 5 minutes. If it doesn't work I would move to pressure.