An objection was raised to my original cable strain relief technique with the PETG motor mount:

The proffered replacement had a difficult-to-print orientation:

Which Meshlab’s Manipulators Tool rotated by 90°:

And that printed without any drama (or support), at least after I sliced it to use a single perimeter thread that could cope with the arch:

Then a few pretty cable ties wrapped everything up in a decorative package:

And that’s that…
Memo to Self: Bang on the ␛ key to get out of whatever mode the Manipulators Tool gets wedged into.
Recent vintages of Slic3r can now do rotations on all axes. Check the contextual popup menu when you click on an object.
And so it can!
I’m pretty sure I’ve never other-clicked on the preview. [sigh]
Thanks for the cluebat whack…