Where do you find down hills in the tri-city area? ;)
Just kidding, my family is from Midland...
Go ahead and attack the seat, but be careful not to take too much out or you will either suffer from a bad case of monkey butt or creat a hole in the saddle that won't let you move around. Try to maintain the original profile as much as possible and you should be able to pull the seat cover tight.
Also, depending on your weight, you may want to go a little more on the sag. You will not lose much in the whoops as the spring rate will not change much. If needed, cut a little off the spacer tubes in the front forks, say a 1/4" at a time.
Finally, the double sole trick sounds good. I would be a little worried about how well your foot fits around the shift lever though.
BTW, what year is your KDX?