I've been through this 3 times (3 states), and the thing to do is take a rain check on your birthday. If this is his first bar, he won't be realizing that in some ways the hard part starts AFTER the two days of testing; the wait to hear the results can be nerve-wracking. (We were in Europe while waiting for DH's last set; he had trouble not thinking about it long enough to enjoy the trip.)
Just sit him down and tell him that you really appreciate it that he wants to do something nice for you, but that for the benefit of the family, he shouldn't worry about it -- he's going to be stressed out enough with the bar to concentrate on. If he wants to give you a make-up occasion later on, that's a good option.
Tell him that you will pick your favorite WDW restaurant and make the reservation; all he needs to do is show up and pay the tab. Then write down all the info including the restaurant's phone number and have him put it away in his wallet. If he wants to call them once the pressure is off and arrange something special, then he'll have everything he needs to do it.