Know his parents at all? You could find out what books he liked as a kid and get some of those for him.
A "guys" diaper bag might be nice, either backpack or messenger bag form (include a gift receipt).
Is he into any sports? You could get him a jersey and a matching set of onesies for the baby.
Netflix gift card? Gotta do something when you're up with the baby.
If you can afford it maybe an iPad or android tablet. I found my nexus 7 super useful in the hospital and when watching the baby at night (again, Netflix). Plus we use it with a webcam as a baby monitor.
Is he the horribly paranoid sort? Get him one of these