I use the app TouchCursor to create a function layer which is activated by space bar. This is great for writing, coding – allowing me to keep my hand in its home position – in SketchUp I find it most useful for arrow key commands (e.g. setting axes of movement / rotation). It has both whitelist & blacklist modes, to control when it is active (or just exit it).
Tapping space gives the usual result. Holding space activates the custom function layer:
space + tab = Enter
space + c= Delete
space + x = Backspace
space + w / s / a / d = up / down / left / right
space + q / e = home / end
I find that I can still type at 100+ WPM without errors, although certain apps create occasional keystroke errors.
See SpaceFN. This could also be achieved with Autohotkey, and I’m sure there are ways to do it on a Mac.
I also remap some keys using SharpKeys, which changes the registry in a reversible way.
Ctrl <–> Caps
Esc <–> `~