Wasn’t sure of what “force fetch” referred to so I goggled the subject and found what seems to be the methods
http://www.fetchpup.com/forcefetch.htm .
Couple of things you should consider (being this is your first dog) that you may already be aware of, but worth mentioning.
Although full size your dog is still very much a baby and pups chew when playing. The labs are even more prone to silly behavior up to 3 years and a male may not reach a mature nature until 4 or 5 years.
Most labs are soft mouthed by nature so do not assume he will be rough on birds until it is proven. Mine play tug of war with the kids and chew toys to bits but have never ruffled a feather on a bird.
Try making your training sessions short (20-30 minutes) and very workman like. Nothing gets a lab more serious then a pocket full of his favorite treats. When he performs well pet him and give him a treat. No roughhousing and loud “good boys” as this will induce a playful response and a pup’s instinct is to mix play with a few playful bites.
He will soon learn to enjoy these serious sessions more then play time mostly because of the treats involved. Bird hunting is not play time for a hunting dog. It is their favorite thing to do but they are dead serious when they are doing it, not unlike any wild animal on a hunt. Your training methods should mimic this.
Get yourself a proper training dummy or better yet a few real birds and never let him play with them. Use only these for your training and always keep your sessions serious.
I’ve only trained a few dogs that were truly rough mouthed and it was sometimes possiable to discourage without going to the extremes of “force fetch” as on the above website. Try him on some real birds and if he really is rough let me know and I’ll give you some alternative methods to try.
Hope this helps MK