One thing to keep in mind is that the brake does take alot of abuse. Whether or not we think so because the motion is so linear. But the friction you mention is in essence the enemy. And then, without the needed friction, we do not get the feeling we are looking for in the brake. (That hydraulic feel). So no matter what ring you place in the groove or how you build out the groove, we are faced with the components at some time giving into some wear. Then the feeling is not the same as in the beginning.
But all things considered, yours is perhaps the least expensive route. Here's why. The screw is a one time piece and will not need replacing unless you wear down the plastic around it inside the cylinder. The o-rings can be bought in quantity up to about 100 pieces once you find the right size and diameter for super cheap, and the internal spring, once you have it (I'd suggest progressive not linear), you will not have to replace this either. (Might want to take a look at an engine valve spring. Might just be what you are looking for. More so from an american engine like a Chevy, Chrysler or Ford. These tend to be beefier and heavier.
I'd be interested to see how you progress.
Cheers.