Perhaps your veterinarian advised you against exposing your puppy while his immune system is developing, but you fear the risks of neglecting to socialize him during this critical period. Though you may not be able to walk him around the big city, you can start a socialization program at home:
Desensitize him to noises by letting him play with an empty plastic half-gallon milk jug or big metal spoon.
Accustom him to walking on a variety of surfaces, such as bubble wrap, big plastic bags, and chicken wire. Put a treat in the middle so he gets rewarded for his bravery.
If his experiences with meeting new people will be limited, you can get creative with costumes. Wear hats, masks, and capes; walk with a cane, limp, skip, and hop.
Take him for car rides with permission from your veterinarian.