I've read that brake cables need adjustment to compensate for stretch. That didn't sound right. Bicycle and motorcycle brake cables used to be soft enough for diagonal cutters, and they didn't stretch.
The rear brake cable on my Radrunner creaked from the day it arrived. It was also spongy. After 16 months, I replaced the cable and housing. The creak was gone, but it was quite spongy. It occurred to me that the sponginess was in the housing. It's longer than the front housing, and it has to curve way around to reach the down tube. Then it goes through three S curves on the way to the caliper.
For two days, I kept the brake lever tied to the handlebar when I wasn't riding. (I had to switch off the battery to turn off the brake light. It would stay on another 7 seconds. Apparently, it draws very little current.)
After two days, I had to tighten the cable adjuster several turns. Now the two levers felt almost the same. I measured. Between first resistance and a hard squeeze, the front lever moved 10mm and the rear lever 15. Considering the length of the rear cable and its curves, that seems pretty good.
Handlebar, your method looks like a great way to increase your braking power without spending money. Excellent idea. I may have to try this on my RW4.
One can also get cable housings that don't allow for flex or cable stretching. I haven't tried them but I've seen a few reviews and they say the mechanical brakes feel more solid, are easier to apply and allow for more modulation of the brakes. Mountain bike reviews of course.