Here's how I taught my Golden Ret. to point...would assume it will work on your lab:
I taught the dog the word stay - that's the first step.
When he was learning about birds(first controlled hunt) we planted birds and worked the dog into the wind toward the planted bird.
When he was close and very excited, he would freeze. At this point I told him to stay.
We repeated this process and it worked.
I reinforced the process in the garage, with a training dummy and rope: toss the dummy and pull on the rope when the dog gets close. Tell him to stay - he already knows this command, right? Release him to retrieve the dummy.
It's actually quite simple, but the dog needs to understand the word stay!
Good Luck...