Once I saw someone post a picture of a bun inside an oven on Facebook. You could always do something like that but send the picture to your family and the father first. I like the box with a onesie idea too. You could even do that for your parents with something that says something about grandparents.
No im not with him and thank you
If you know the gender by a plain pink or blue shirt and write congrats everyone on it and either wear it around them or send them a pic of it or the ultrasound. Is it safe to assume you're not with the father, being this far along and he not knowing? Or is he away? If hes away and has a mailing adress pack him a small box of bibs, baby onsies about worlds greatest dad or daddies lil man or girl. And include an ultrasound pic.