I too am having the same problem with cutting piki's nails. I did manage to get one cut using some nail scissors but he doesn't like being held up on his back for a long time as he wiggles a lot. and i dont really wanna do em all in one go.
I did ask at Pets At Homewhere I got him about nail clipping service but they only seem to cater for syrians and not dwarves
I might try the terracotta idea though, as I did try sandpaper wrapped around one of his wooden toys then i noticed bits on his feet were being rubbed raw/balding so i took it out and now they've gone back to being furry feet now!