I have similar need to only open my non-dominant eye to see the bubble without breaking my cheek weld. Maybe it's my massive head, but I can't see anything well that's in the centerline of the rifle while I'm in my scope.
The only bubble that was easily visible to me was the Flatline part I linked above. This was after trying Vortex and several other Flatline parts that attached to the scope tube.
I like the fact that it mount to the pic rail and can be folded in to clean things up when not shooting.