Send him flowers or balloons at work; decorate his car while he is at work so he sees it at lunch time or going-home time (get a co-worker in on the secret and ask him/her to photograph DH's reaction!!). Call him and sing Happy Birthday--with your baby "singing" too. Leave it on answering machine if he is not there.
We have been known to send people 30 cards for thier 30th b-day; 50 cards for 50th, etc--one per day, leading up to "the" day.
You could send a bunch of different e-cards (cheaper than paper ones through the mail).
I don't know where you are--could you go for a walk in a nice park, along a river, etc before dinner? Just a thought.
Good luck and have fun
K. Z.