If it’s just simple constipation you might be able to give him some Osmolax (like 1/8 to 1/4 tsp) mixed in wet food with hot water until you get a good output. Half a Microlax enema (well lubed) will get results fast and hopefully help him pass all of it.

However I don’t know everything so maybe don’t use these if something like a blockage is suspected.

I hope things resolve soon, emergency vets aren’t cheap :(