You could do something
like what I have done, to send a different voltage to a single analog input for each of several buttons. My work is set up for 32, but you can do any. But from scratch, it's cost me a little more than the price of a new brain. The parts cost about 25$ total, not including getting a custom prototype PCB made, but it can be done more cheap. Also, you may get unexpected results (press defrost plus recirc, and the compressor may turn on

) if you press more than one button at the same time.
As for the servo/PWM route, you're going to need to do one of a few things:
a. wait for an analog output from the fusion dudes.... and keep in mind, when taking a parallel style output device and providing an analog output, you will sacrafice a few outputs, who's quantity will vary depending on the resolution required, and what's available.
b. build/find something that can drive PWM....
c. find a servo that does not require an analog input. They do exist. Basically one voltage level will drive the motor in the open direction, another will drive it closed. Then, with a PBR (position sensing potentiometer) sending an analog feedback signal, FCC can be taught to stop the motor (yet another voltage) when the feedback resistance (and thus it's voltage) is at the pre-assigned level for that particular position. GM makes these, for just this application. The voltages can be created with just a couple digital outputs and a few resistors.