Emily,

I wish I could give you some useful advice.

What about feeding him at night? would that make a difference? Can he get out during the night to do his business?

I think that site that Amy pointed you to might give you some good pointers, and ideas where to start. I would read up, and then contact the vet.
Riley might have a sensitive stomach (or something like it) which makes him poop alot. They would be able to help you handle it better I am certain.

{{{{{hugs}}}}}