I'm not hugely familiar with your car but I believe there will be some sort of switch on the brake pedal that will send a signal to a solenoid to release the button so you can shift it. Without the brake on the manufacturer will not want the car to shift as it would cause damage to the transmission. Sweet Jesus, this Rum and Coke hit me hard. I'm having trouble typing!

I had this problem with my 2002 Odyssey. I don't know if they are exactly the same design but the basic idea is the same. The brake lights wouldn't come on but the horn worked (rules out the fuse located under the hood, passenger side compartment). Could not get the thing out of park. I temporarily used the emergency unlock switch located on top of the steering column. (a small plastic tab can be pried out with a screwdriver and a key inserted pushes a button down releasing the shift lock. its in the manual.) The culprit was the BRAKE STOP SWITCH located above the arm of the brake pedal. VERY easy to remove and replace. And the part was at an auto part store. (fairly cheap too). The switch is a safety feature so a kid doesn't slip the van into drive accidently. Its just above the brake pedal, about the size of a C battery with a wire connected. First take the wire off by pushing the tab in on the wire connector and pulling it off the switch and tucking it away somewhere. Then get a wrench and loosen the lock nut a few turns, then unscrew the switch from the bracket. (it will be more obvious what to do when you have the new part in your hand). Then take the new switch and screw it into the hole. Push the brake down and feel on the other side of the bracket to make sure the button just clears the bracket so when you depress the button completely it is flush with the bracket face. Then get the wrench out, tighten the new lock nut and plug it back in. And hey, you fixed it. Check to see if the brake lights are working and you should be able to put it into drive by depressing the brake pedal.