To be blunt, under _no_ circumstances should sponge neoprene be used
on any piano, for any reason!  I have not yet seen this material made
by any manufacturer stand up.

I have done plenty of tests in the past and found that the material
seems fine in the beginning but then it gets hard, and will create
a memory, meaning that if you push your finger into the sponge the
depression will stay there, not to mention many other problems.

Bottom line: the correct and appropriate materials are available,
use them.  Respecting the instrument will always pay off at the end.

Musically,
Robert Loeffler - Roberts Musical Restorations
http://www.robertsmusicalrestorations.com/ 
http://www.youtube.com/user/RobertsRestorations