A rotating 45 degree prism on top of your bubble level so you can see it when the head is at eye level. Rotating so you can rotate it so if you are standing behind or to the side or to the front when you level the head, you can see it.

Right now, the only way I can level the head is to have the head at least 6 inches below eye level and even with strong glasses, it's hard for these old eyes to see the little bubble in the little circle -- it looks like there's a bunch of both of them.

And if the head is 6 inches (or more) below my eye level, then the viewpoint of the pano can look weird -- which is, in a sense, appropriate considering who the photographer is.