You can get him one of those toy cars. I'm not talking about the micromachines one. There are these model cars which go for around 60 bucks upwards. Get him some BMW model. (Check out Toys R' Us)

Write a card somewhere along the lines of "This is just a reflection of what's to come!" and put it with the toy car. Box it up and wrap it.
Get one of your hottie girlfriends to work with you.

Take leave on that day. When hes at work, hand deliver a card to the reception, tell reception to forward it to him. In that card, give him instructions to a restaurant of your choice. Pick a relatively quiet place.
Specify time.

Because you're on leave you can go slightly earlier. Pre-order the food and make sure the waiter knows that he only prepares the food upon your signal to him. You've known him 5 years, you should know what he likes and dislikes by now.

When he arrives, make sure he is comfortable. From under the table, miss call or send an SMS to your hottie friend who is across to room dining (Yeah you probably have to pay for her food )
She'll walk across now, put the box with the car inside, peck him on his cheeks and say "Happy Birthday" and walk off.

Signal the waiter, wait for meal.