Definitely put him into a breeders net and fast him.
It would be best to take him out of the tank but since you don't have any spare ones, the breeders net would be best for now.
Hopefully after a few days of fasting and then giving him some pea he will poop.
You could also try giving him an epson salt bath. I've used about 1 tablespoon per gallon. Dissolve the salt in the water. Leave him in for about 30minutes. That might help him clear up his system as well.
What does he look like when you look at him from above? If his scales aren't sticking out, then hopefully he is just very constipated.
If his scales are sticking out like a pinecone, then it's dropsy which is being caused by a bacterial infection and you'll probably want to treat the entire tank with something.