Yea maybe implement something like natal for your PC to recognize each movement in your body as a hotkey, so while were working it actually looks like we are dancing.
And then some people will invent a way to actually make the dance look decent, and produce amazing artwork at the same time!
More exercise, less RSI, win.
Anyway to the topic poster, I know you are looking for a non-3rd-party solution but if you cant find one then I recommend http://webpages.charter.net/krumsick/
for simple keyboard remapping that doesnt take up any resources.
Or another solution, dont use alt with your thumb. Actually you just gave me a good idea to improve efficiency for myself, I got into a bad habit of using alt by moving my hand down from the QWERTY area when I could replace caps lock with alt instead. Thanks