As cute as it is, don't be afraid to say "no" or cut the game after one or two tosses of the ball
Once he realizes that while you're at your desk it's work time for you and quiet time for him then he should stop bugging you.
I'm one of the people that when my dog brings me something it's a good thing, but when I'm on my computer and I get a nice juicy drooled on toy dropped on my keyboard I realized there had to be a happy medium. So when I'm busy I will toss the toy twice, then it's game over and I simply tell him 'all done' when he comes back. When I'm finished my work then I call him and tell him to bring the toy back and we'll play, he's gotten the concept that 'no' doesn't mean 'never' but 'later' so he's learned patience and to wait until I'm finished
Jasmine - Female Miniature Poodle - born Aug 15, 2010
Loker Delgado Von Stalworth - Male GSD - born Jan 26, 2012
Koda & Zazu - 5 year old male cats
Alex - Male Cocker Spaniel (rescue) - RIP Cuddlebug 2007-2010