I rigged mine last week to do pretty much what you want. With the glovebox area removed you can reach in and remove (pull back) the rubber cover that covers the 2 center vents. Twist and pull the vent hoses out and move them to the side. You can then see the vacumm control that opens and closes a vent. I used a curved needle nose pliers to wiggle and wedge and pull the washer (securing washer) the holds the pin that connects the vacuum control arm to the vent. After you have seperated the arm from the vent pull the vent open and air will flow through it. I wedged the opened vent under the vac control arm to keep it open. Replace the vent hoses they will twist then lock into position ,then the rubber cover you removed and air will be permanently be directed through the center vent. You will need a small flash light to see inside the dash. take care It can be tricky or easy. In Louisiana I did it to keep my windows from fogging up when the A/C was on. It's to dam humid down here. This Should give a good direction to go. RAY M 1980 300d