I'm assuming you've already got a little one? Perhaps putting them in a t-shirt saying big brother/big sister and having them walk into the room to see Daddy? That way it gets your little one involved too xx
I bought little booties on Etsy and a babygrow saying 'You're going to be a Daddy' then 'I love Daddy ok the babygrow' x
Unwrap a xmas cracker and replace the joke with a message announcing the pregnancy. Wrap it back up and pull the cracker with him.
Put a bun in the oven and ask him could he go take the turkey (or what ever you like). He will be confused and then hopefully the penny drops😂. Congratulations