Tie a stick to their chest and neck sticking out 7" in front of their nose and then put a hot dog weenie on the end of it.
No seriously put him in good sign and let genetics take over, if he won't hunt, find another dog that will.
that is the bottom line...but you can coax it out of them is they are going to have it...I need to see a progression in a pup according to age...if I don't see it the pup doesn't stay...