I don't have RSI, but it seems to me that rotating your wrists to press Ctrl with your pinky is one of the larger parts of the problem. I prefer to press Ctrl with the side of my palm, but that doesn't work on some Lenovo and Apple laptops which Fn is at the edge of the keyboard.
Just remap Caps Lock to Ctrl, problem solved.
If using Linux, simply add `ctrl:nocaps` to the XKBOPTIONS= line in /etc/default/keyboard, e.g.:
XKBOPTIONS='other:options,ctrl:nocaps'