Since there are different solutions present, I’ll just go shortly through the steps on how to fix your G600 (as I did it weeks after I asked this question). Please do not push or pull the plastic or anything on your mouse, because it might break and won’t fix the problem presented in this thread. Each step should be easiely done without to much force.
1. remove the patches below the mouse (I used a sharp knife and cut through the glue). Please note, that this process is possibly irreversible. Trying to glue the patches back on might only succeed with luck AND skill. But keep in mind, that you won’t notice the difference of missing patches to much, after a few days (I’ve tested both with a mousepad).
2. Undo the screws carefully (beneath the patches). The mouse has some connecting elements that are all powered via a cable from the mainboard, meaning you should remove the cables carefully and put them back on if you reassemble the mouse.
3. Use a soldering iron and remove the broken parts (This could take a few more tools to fixate the mouse). Please at least open a window while you do so. You can easily take parts from another spare-mouse to replace the parts, as most parts (that seem breakable) have a universal size. Additionally you can remove a lot of weight from the G600 if you want (there are weight pallets inside the mouse, this is a personal preference, you could even add some).
4. Undo step 2. Is you can/want also step 1.
I hope this summary helps a few people out there who still use this awesome mouse