Cork, been done! - I stole the idea off one of those greenies wood surfboard forums.
I used 5mm thick floor mats from Bunnings but they add a bit of weight feel a bit thick underfoot so I bought a roll of 1.5mm thick self adhesive to stick on but have not had a chance yet to stick it on.
But I must say Cork is the grippiest grip I have ever had.
So get a grip and use cork!
Rich