How to cut the seat foam and add extra padding to the stock ZRX seat. This mod removes the forward slant.
Cover removal / Staple removal

Remove the seat, turn it over, and remove the cover.
Give the staples a little lift with a screwdriver. This makes it easier to grab them with some pliers. Grip the staples tightly and yank 'em out.

It's best to leave a few staples in at the back edge of the seat, and the cover attached, so alignment is not a problem after you are finished cutting the foam.
Foam Bottom

Mark an area with guide lines. Removing foam from this area on the bottom of the seat makes the seat more level on top.
Slice that turkey!

It's as simple as slicing a turkey...
Don't take too much on the first cut - never more than 1/4" at a time. Take a little off, put the seat base and foam on the ZRX, and try it out. Make a few thin cuts, and test it each time.
Cutting more off is much easier than putting it back on.
Seconds, anyone?

After 2 or 3 thin cuts toward the back of the rider's seating area, remove a little from the front of the seat. These cuts help level the seat from left-to-right.
Do a friend a favor.

Mark an area under the passenger seat and trim the foam to make the seat more level.
Add a little foam.

Add a piece of foam to the top-front of the seat. This helps make the seat top level.
Top foam location.

Put the foam in this area before re-installing the seat cover and seat base.