I had one that would pass urates a lot when I held him. I think it just has to do with the handling kind of massaging it out of them, as gross as that sounds. Or maybe something to do with human body heat, too.

As for remedies, the only thing I can think of is to make sure that he has gone to the bathroom before you hold him. Like others have said, they don't go that often and because of that it should be somewhat easy to predict when they are likely to go, so maybe try to work handling time around that accordingly?

How long do you usually have him out for, and does he do it EVERY time? Does he ever poop IN his cage?