I was thinking about this recently, too. I remember that Chad Waterbury has stated in several articles how the size of mechanics forearms made an impression on him. Well they most likely don't use wrist rollers. Other than lifting heavy weights (which we already do), the key difference is that they tighten and loosen nuts; lots of them; some really big, high-torque nuts 'n bolts; "high and low rep" (long and short).
I intend to wander down to Lowes one fine day and buy some metal, rubber, wood etc. to make something that will compress, but only with tremendous force, then tighten and loosen nuts and bolts through it accordingly.
(Or I suppose I could go round the Wal Mart Parking Lot and take peoples wheels off their cars. Do you think the police will be sympathetic when I say "but I was only trying to get bigger guns, officer?").
Has anyone else considered, or even tried this approach (no, not the Wal Mart thing...)?