I often do this by moving the detail control points, but you can also do this by starting the pan, then holding shift (if I am correctly understanding what you are asking for).
Hey Sam! Thanks! The “pan - then shift” works fine!
For some reason I have not thought of pressing shift after I had started panning.
(I have only used Rhino since '96 you know, so still lots of things to learn… )
It is kind of a weird convention, but almost all of Rhino’s camera controls respect the start the move first then shift to constraint. I most often use it for Ctrl + Alt + RMB pan in a perspective viewport when I want to keep the target at the same Z height as I look around.
I do the same thing, I find it more safety than panning inside the viewport.
One improvement could be, when selecting the detail( just one click) adding a point at the centre of the detail, that would let us grab or move the content without moving the frame, just to “focus” on another place of the detail. Indesign does this and it is quite handy.