When I was pregnant with our first, we told the grandparents at Christmas..... I don't remember how we told his parents, but for my parents, we found a ceramic cake topper of a stork (You know, the typical image of the stork with the blanket "sling" in his beak, holding a baby)... if I remember correctly, it even said "Guess what?" on the base...
Anyway, we wrapped that up and gave it to my parents at Christmas....
My M. got the message RIGHT away, but my dad was a bit more dense..... he was the one that actually unwrapped it.... and was looking at it, with that typical expression that you have when you don't really know what to say about the gift you were just given... "Oh, That's nice..." kind of thing.... my M. asked him.. "What is it? (trying to give him a subtle hint), and he said... "A bird...." then my M. said "What kind of bird?", and my dad said... rather puzzled... "A ..... stork?" I can still hear his voice (30+ years later) rising in surprise on the last word.
So... maybe you can find something that is a typical baby item.. (new rattles, new bottles, bib, booties, etc,) and make up a "dad's baby care kit" for him to unwrap?