WASD -> Up/Left/Down/Right ZCRF -> Home/End/PageUp/PageDown Space -> Backspace Tab -> CapsLock
Not tested yet
Check for F keys was only requiring one of F1 or F4 to be pressed..
Compile a small C function for checking pressed keys and entering BSL (Bootloader) mode and add the code to the end of the original binary. Call the function from the code checking fn + F* keys.