I like solid bottoms in my cages, for all the same reasons mentioned.
I have had a couple that got into the habit of peeing on shelves. I put them in shorter cages so they wouldn't have so far to go.
I have even seem one back his bottom off a shelf a pee down to the floor.
As they are all so different in there likes and dislikes, I'd keep playing around with the cage until I found the right set up for each chin.
If they were peeing on a certain shelf, I'd remove it or block, and see what they do.
If you put in a pine bottom as Jamie suggested, or even get a pan made to fit that should solve your problem, if it was caused by the wire bottom.
If it's just one of "those" chins you'll have to keep playing and modifying the cage until you find what works.
Just thinking, what if you put him in a small cage that he has to pee on the floor for a few days.He might get the hint.