First I want to say that Al is a cutie! Is he an albino?

Now about the exercise ball, I say keep trying!
Brownie is my lazy gerbil who doesn't like to run in the ball much either.
Sometimes just give the ball a gentle nudge to get it started.
Also try putting Al in the ball at different times of the day.
I found that Brownie will run more in the morning in the ball instead of in the afternoon or evening.
I also find that if my cat is watching the gerbils roll around in the balls that it motivates the gerbils to run over her toes!
Just make sure that you supervise other pets with your gerbils when they are running in their balls.
Good luck and keep trying!