If you can measure the resistance values, then possibly yes. If the 3 values are out of range by only a little bit, then you could put a resistor on the line and make all the values within range. You would have to carefully program Hijack to use a
completely new set of translated values, but it sounds like you're on top of that and shouldn't have a problem figuring out how to do that.
Not sure how your stalk gets its data to the Sony interface, though, so I'm not sure if "out of range" is the reason you're having the problem. I'd be curious to know more details, because my friend Tod's stalk converter isn't working 100 percent, either, and we haven't yet cracked the dash open to work on it a second time.
Next question...
If you've got a computer in the trunk, why bother with an empeg at all? I mean, I'm impressed that you're using my EmpegFace to control the empeg in the car, but if there's a computer in there then why not just put all your MP3s on its hard disk?