No problem. Thank you! 
From this answer I’ve learnt about camera.detachControl().
And if I combine with scene.onPointerDown/Up and scene.onPointerMove I might be able to fudge the movement. Do you think that might work? I can’t see an attribute on scrollViewer at the moment that allows you to set the scroll position… Assuming you can “manually” set it, do you think there are any gotchas that I should look out for if I attempt that approach of “manually” linking pointer movement to the scrollViewer?