I used to have a Slim when they first came out. I added Pearce grip extensions to make it more comfortable to shoot.
The magazine body on the Slim looks almost exactly like the G2S magazine body, so I decided to try the Pearce extensions on the G2S. I bought a couple off ebay that were $10 for two and free shipping. Initially they fit in place of the factory bases. The locking tabs on the factory bases are round and the slots on the Pearce bases are square, but they fit right in. The only problem was that the top of the Pearce bases had be to ground down about a millimeter (more or less) for the magazine to properly lock in place. Did this by hand out in the garage using the grinding wheel on a cheap chisel sharpener. Results were pretty good, although I won't be satisfied until I can put some rounds downrange to see how recoil affects them.