How about trying a long lead? (like a clothesline rope.) Then he can have the "freedom" of not being 6 feet from you...but when you say "come" you have the ability to enforce it (or at least get the momentum headed in your direction.
Another idea: 2 people inside, playing a simple game of hide and seek. One has the pup, the other "hides" (in an easy spot) and calls for Jackson--he comes and gets a jackpot treat. Other person calls, Jackson gets treat. First person moves to a new spot, calls, treat, etc. Puppy keeps running back and forth to get the treats, but is also responding to the command (even if he doesn't realize it--yet.)
Hope these ideas help a little.
Another idea: 2 people inside, playing a simple game of hide and seek. One has the pup, the other "hides" (in an easy spot) and calls for Jackson--he comes and gets a jackpot treat. Other person calls, Jackson gets treat. First person moves to a new spot, calls, treat, etc. Puppy keeps running back and forth to get the treats, but is also responding to the command (even if he doesn't realize it--yet.)
Hope these ideas help a little.