fredo6 - you are a hero to me!
another idea:
all the "on surface" tools are already existing tools of SketchUp applied to a surface, right?
and when you succeed in creating all the other tools (tape measure, circle, polygon...) our toolbar gets quite large.
would it therefore be possible to just have one button in the tool bar (plus a shortcut key to toggle it on and off) that switches the use of SketchUp's native tools to your fabulous on surface tools? thus all my shortcuts would apply to your tools too - I only have to press the "fredo6 button"!