Hi Phil,
What I had in mind is rather similar to your design (but with one eye on simplicity, cost and ease of manufacture) I was thinking of replacing the machined "cage" which goes around the eyepiece with a reusable cable tie.
That would probably have worked great for my first variant that attached around the objective cylinder!
For the attachment ring, a cable tie would not exclusively be stressed in "pull" direction, but it would also have to carry a bending moment, since the attachment block doen't have a corresponding surface on the scope to be pulled against. Basically, it's only supported on its lower edge.
That's why I think I need a big and stiff vertical ring. It's not actually an machined artifact, but rather a 3D printed plastic part, so the price is not going to be so bad. The entire assembly is going to be less expensive than my original objective clamp with the "tower".
"One size fits all" would of course be a great accomplishment, but I think the method of attachment is really limited to scopes with a Kowa-style accessory thread, and I guess only the Kowa TSN-883/4 have this. (I haven't actually checked other Kowa scopes ... on pictures, it's hard to see since it's hidden by a smooth fairing ring. I'd probably have to download and read the manuals.)
The attachment block itself has a 9-sided polygonal mount, which works great for the 40 degree angle of the TSN-883, but wouldn't work for a 45 degree angled scope, which I think is more common, or even for the straight TSN-884. (If the angle had been 45 degrees, I could just have used an octagonal mount that would have been good for straight and angled scopes alike.)
However, not to say that the cable tie idea wouldn't work well with other scopes. If you have an eyepiece with a fixed cylinder, that would probably work just fine with a cable tie (or two) on any scope. (With the zoom eyepiece on the Kowa, the entire eyepiece cylinder rotates when zooming.)
If you have an eyepiece cylinder like that, you could post the dimensions here, and I'll see if I can come up with a simplified version of the attachment ring.
I guess all it would need would be two slots on the backside to run two cable ties through (or one big one), and maybe the backside should also be curved to better conform with the eyepiece contour.
Regards,
Henning