The ball is obviously an A Grade reward. Jas needs to work for it to gain access, eg recalling when asked. For it to retain it's A Grade status, access needs to be limited. If you only keep it for recall - you are already doing this, but if he gets growly when the pup comes near then the ball needs to disappear before the pup appears so that he doesn't connect the pup returning with the loss of his beloved ball. If he is then calm and quiet as pup goes on the lead, he gets the ball back to carry home as a reward.
My oldgirl had a squeaky ball that was her ultimate reward, she would do anything for it, but she only ever got to play with it for very short periods of time and in training, just being able to give it a quick shove with her nose to make it squeak was a highly motivational reward. If you are canny, you can use Jas's ball obsession to your (and Pup's) advantage here.
Unfortunately, now we have the pup, he gets all snarly when I recall the pup because he's within a metre of his beloved ball. I don't want his attitude to stop the pup recalling, so any suggestions? At the moment, I get the ball out, throw it a couple of times after getting Jas to sit and let me touch his collar, then I attach the lead when I'm ready to go. He straight away picks up the ball to carry it home, which I always allow. Then I call the pup, who happily trots over, ignoring Jas and his ball. As I go to clip his lead on, Jas lunges and snarls, the pup cries and cowers, and I get a bit growly myself. If I lead the pup first, Jas won't come to me at all <sigh> The pup is not trying to steal the ball, and gives lots of submissive body language in a 'Hey, big dog, I'm not going to even look at your ball, ok? I'm just going to lick my lips and look away and wag my tail and lick the human'. I'd love to ditch the ball and get a better recall some other way, believe me, but this dog will not recall for food (even liver/sausage/cheese/tuna).