Not sure how old your pup is.. But, be sure to praise him when he's gone potty on the pad. Its also a good thing to associate a "phrase" with it. "good potty" "potty on pad". I too work all day and Meka was in a similar situation as far as being confined to an area with her pad, etc... When I came home, I would praise her for doing good ("good potty"). I would let her out to play, feed her, then after 20 min or so, tell her "go potty" and she would go to her pad. I definately would not stand over him expecting him to use it, because after being without you all day, all he wants to do is love you
Just be consistant and all will work out just fine