We've done the cake a couple of times for mine and my daughters birthday. You can reserve a cake at the podium or check in when you arrive to dine, or you can have one with your wife's name if you reserve in advance.
You can call 407-WDW-DINE and they will give you the number to reserve the cake. Sorry, I didn't have it written down. Be careful however when you talk to the Disney Dining. The way the girl phrased it to me the first time was that I could not call until 48 hours before the event. So I called 2 days before and was told I'm not supposed to call that late to reserve a cake. They were still able to get us a cake with our daughter's name and 2 candles (she turned 2, normally they only do 1.) If you're going this route, be sure to call well before the event!!
Oh and the cake? Very thick with frosting but we like that kind of thing!
Tonya