Too bad. Get a mouse for SketchUp jobs. The quick access to the navigation tools with the middle mouse button is indispensable. Look at the SU system requirements where it (not incidentally) says "...3 button, scroll-wheel mouse".
However, if you insist, the Orbit (and Pan: Shift+Orbit) tools have a special behaviour when launched as tools used by the left mouse button (or equivalent of the touchpad): whatever tool you were using before, if you press the Escape key while in Orbit or Pan, you will be put back to that tool (so no need to select that particular tool gain).
But this is really a "hidden" and rarely if ever used feature since (as I said and also suggested by the developers), most people use a proper, 3-button mouse.