This is the original setup. The brake lever has a metal loop that slides over the bars and threads onto a screw which can be tightened from the front of the lever and thus pulls the loop into the body of the lever and tightens it to the bars. I wanted to move to something that would separate at the back. I am aware that such levers are available for purchase, but that is not what this is about... at all.
The first thing I did was to remove the loop so I could replace it with something that could separate.
The obvious replacement for the loop was a small hose clamp. I bent it to match the shape of the loop with a protrusion that would insert into the body of the brake lever. At the end of this protrusion, I drilled a hole to accomidate the tightening screw and rectangular nut that would serve to draw the hose clamp into the body of the lever and thus tighten against the bars.
This view shows the hose clamp installed into the brake lever. I got this part tightened all the way down until the protrusion was totally inserted into the complementary shape in the lever body and what remained was rounded to contour the bars.