S.S.
Get him his own baby doll with some of the accessories. I know, I know...girl stuff. Having worked in daycare, I can attest to the fact that boys like playing with the dolls too. Think of it as beginning preparation for when he one day becomes a dad himself. Make a bed out of a box and tea towel. Bib, diaper, bottle, spoon and cup... he will see Mom and Dad using these things on Baby. Let him have his own such items to mimic with. It will help him to be part of the new goings on... and eventually to 'help' with his own real sibling.