Here's some information on the software I have developed for the operation using left hand and foot.
Key input recognition with python on Raspberry Pi
Input key to VK_Key convertor on Windows 7
C++ Builder Code
v0.3 @ qiita with articles in Japanese
Software features
Mindmap @ mindmup
https://atlas.mindmup.com/2016/05/eb82b840f1b60133b5fe0698cd91bbc8/footinput_softwaredesign_160501/index.html