Chuck,
The DX7 doesn't have throttle expo "although it should", but you can sort of fake some expo in anyway. I had the same problem so I started playing with the offset and servo throws. I found that if you offset the center big time and then adjust the throws to give you the full range of motion you can make the bottom half "or the top" less sensitive. On mine the first half of the stick only moves the throttle a quarter of the throw and the top half moves the other three quarter or there abouts. You'll have to adjust the throttle servo arm but that's easy...
There's my two cents... hope it helps.