Take him in the shower with you a couple of times a day just to get the intense steam of a regular shower, not like in a steam room.
Use the nasal spray made for babies and then suction out the snot with a snot sucker. There are video's of how this is done properly on youtube. I found out I did it wrong but I got so much stuff out that I had no idea.
Put a ultra sonic humidifier in several rooms or put a large pot of water on the stove and let it simmer to put moisture in the house.
If it sounds like he is having trouble getting the mucus up then turn him over to where he is slightly upside down, cup your hand, gently pat him on the back and around the back of his rib cage to loosen the goo. That's what the nurses do when a little guy has pneumonia. The cupping of the hand is important, a flat hand just hurts.
I might go ahead and see the Pediatrician just to get a prescription for an expectorant if they felt it was needed.