I've just got hold of a replacement seat for my VFR to see if I could lower the bikes seat height a little and thought you might be interested in how it turned out.... I removed all the staples holding the cover to the plastic base frame, then set about it first with a sharpened up bread knife. This worked, but it was rather inclined to take out uncontrolled chunks of the foam. I then thought I would see if a small angle grinder might be more successful, possibly giving better control of the operation. It worked much better. Drawing the grinders disk backwards from the sponge produced a perfectly smooth surface and took the material off in a very controlled way.