I have a lab too, who naturally retrieved in the water, but once we started on upland she would run over, pick them up, and carry them a few feet in some random direction, then sniff them and roll them around in frantic excitement. I read all about force-fetching. I'm not sure how much you have to follow the letter of the law to officially call it force-fetch training, but I basically fixed this by INSISTING that she pick up and bring to me EVERYTHING and ANYTHING that I asked. This was as simple as a ball or bumper during play/exercise session, to random things in around the house. As suggested above, I got a frozen duck from a farm and tried it. No problem. SHe would bring it to me first time, every time. I was happy, then we went grouse hunting - same problem, she wouldn't bring the birds consistently (although if I brought her to heel, got her focussed, then sent her to fetch it she would do it, more or less). I decided that this might be because the gun got her SO EXCITED that she lost her focus, so I added a shotgun to my training with the frozen duck (which is harder to do, since I live in the city and have to go out to a training field to do this). She WAS more excited with the gun, but still brought it back without a problem.
The current status is that she still has some troubles, but she is improving with a combination of insistence on retrieving on command, and with LOTS of encouragement when she does. To be honest, I didn't see this as a big enough problem to bring myself to pinch her ear or do the toe-hitch etc... to correct it, although I'll admit to being a bit of a softy with her (she's a very mild-tempered lab). My theory is that it's the HOT bird that makes her lose her concentration. I think that the sensation of a freshly killed bird in her mouth is quite overwhelming, so she drops it, looks at it etc... instead of fetching it. I think that this will improve over time as she gains more experience with more birds. The only time she refuses now is in the field with a fresh bird, which I deal with as follows. I go to her (wher ethe bird is) straddle her (so that she can't back away) and then encourage her to "take", then "hold". If she doesn't take I have used the ear-pinch or just opened her mouth and put it in. If she drops it she get's a "wrong" and we start again. Once she's holding it I get her to walk at heel with it using "hold" to make sure she doesn't drop it. Then we do a short retrieve with it, then farther away, etc... It takes a bit of time away from the hunt, but it seems to be working. A local trainer has pidgeons that he puts in these little mesh "sleeves" and hides in the grass, and has offered to bring me along when he trains like this. I think this will also be a great tool to give her exposure to holding live birds and fetching them to me.