I think you should go talk to them, and tell them you have a great home for the pup, where he can live inside.
I just did this, a friend of mine, her hubby got two puppies, left them outside for days when they were babies. When I asked why they were not allowed in the house, he said because they were not houseboken (duh....how could they ever get house trained if they are not allowed inside the house!)

So...long story short.....it took me almost 6 months, but he finally gave them to me, and I found a home for them both (they stayed together)

So....I think just talking to them would be best, if that doesn't work, then call the humane society.