If your training for working purposes using one to distract to get the other won't help you in the long run. We were taught to face away from the dog crouched on the floor and as someone else has said make what ever you are looking at interesting (lots of ooos and ahhs). when he comes to investigate praise for coming and hold him IGNORE the ball, once you have him back on his lead let him carry it for a few paces then ask him to sit and present, you can then remove the ball and offer the treat in exchange for good behaviour.
Its a real struggle not to want to chase them and grab whatever it is they have but in the long run its worth the patience.