Finally received my tripod-mountable, magnetic frame,
"2.8x LCD Viewfinder Loupe for Nikon J1" from eBay seller
jinfinance today, and as I suspected, it fits the Q quite nicely. There is a slight offset to the right, but no buttons are obstructed, and only a slight slice of the LCD is blocked. The mount has fore-aft adjustment, but only a little side-side, so I think a drill can fix this. The view is very clear, and the interior is well-flocked against reflections, but the loupe is pre-focused to the distance of the frame, so there is no diopter adjustment possible.
The reason I went with this kind of loupe is because it is cheaper ($15-$25), but doesn't require sticking anything with adhesive to the camera (I hate cheap adhesive on my stuff!). Instead it uses magnets and a metal frame that attaches to the tripod socket (but has its own socket below that, so it can still be mounted to a tripod!).
I added this type of Q-loupe to the accessories database, and
provided a review here.