Hi Fred, you can set it with the "Area" zoom tool on the viewport bottom toolbar. For that you first pick a center point and then area size and the center point you pick will become the new rotation pivot point.
You're welcome Fred! Also you can paste in the following script for the "command" part of a shortcut key, this one will do one point pick and set that as the 3D view's rotation pivot point:
script: /* Set 3D view rotation pivot */ var p = moi.ui.createPointPicker(); if ( p.waitForEvent() && p.event == 'finished' ) { moi.ui.mainWindow.viewpanel.getViewport('3D').targetpt = p.pt }