Achille,
Unfortunately, the closest I've been able to achieve to what your after was to set up two gestures.
Five Finger Move -- Set to a Pan Shortcut defined in your work environment
Five Finger Click (or Tap) -- Left Click.
ArchiCAD will Grab and Pan as you make and hold the five finger click. Unfortunately you have to release the Pan mode with an additional tap to the trackpad once you are finished. Maybe somebody else can come up with a better method.
