A few months ago I decided to replace my Logitech G500s with a Corsair M65 RGB Elite on the main system, so the G500s could be used on any of the other systems if needed.
I've been using the M65 for many hours, but after some time I noticed that there was not enough support for my ring finger and the little finger is always dragging over my mousepad. This is not a big deal for a short period of time, but gaming a few hours causes some numbness in my hand from trying to hold my fingers up. On the G500s is a little edge next to the right mouse button, big enough for the ring finger automatically holding the little finger up a bit. On the M65 the whole top is a button, so no place to rest a finger other than pushing it to the side of the cover.
To fix this and enjoy the mouse even more I decided to get some 2 component plastic and add a support to the right side of the mouse. First I had to take the whole mouse apart to get to the clips holding the right plastic cover in place, forgot to take pictures at that time, and removed it. I drilled 2 holes for screws in the cover, so the screws could support the weight of 2 fingers and the big chunk of plastic that I was going to add. After that I molded the plastic to the cover and gave it a shape I thought would be good to rest my fingers on. To "bake" the 2 comp plastic I placed the support on a GPU running Folding @ Home, nice and warm
After installing the modded support and giving it a quick test I was very happy with the result. It doesn't look perfect, but it's impossible to see that with my hand on the mouse. The added weight makes it feel much better in my hand, and no more numb fingers! According to Corsair it weighs 97 grams in its original state (not sure if that's with the little weight inserts), and after the mod my scale said 159 grams. The added width is 15mm in the middle and 20mm in the front and rear.
Here are some pictures: