I just purchased a CW40 and began looking for a grip extension to give my pinkie a little extra grip. Pierce did not show that they had one, so I searched the internet for any options. I found none.
Then I noticed on my desk that I had an extension from a Ruger LC9 that I had replaced with a +1 extension. It was just sitting there waiting to be tossed in the extra parts bin. I checked it out and found that with a couple of modifications it fit the CW40 beautifully.
The first modification is to drill a new hole directly behind the existing hold with a very thin boundary between them. The second modification is to grind off a bit of the raised back end of the Ruger base plate. It curves up a bit in the back. Once done, the fit is actually closer to flush than the stock base plate.
The Ruger LC9 Finger Rest Extension is available for about $7, so this is a no-brainer for anyone wanting that extra bit of grip.