Using this post from the technical library as a guide: topic6243.html I pulled the seat cover about 3/4 of the way off and went to work. I chose to extend the cut back to about 3" from the seam in the seat and to follow the same basic curve as the stitched seam.
Here is a photo of the final result after about an hour of work:

The results are actually better than I expected. My wife's feet are now almost flat on the ground and the difference in seat comfort after removing about an inch of foam is not even noticeable.