You are never going to get great braking from the rear in my opinion. Some have reported good success cleaning and greasing the pivot point. I don't notice any difference between my Interstate with boards and my Standard with pegs.
I disagree that you'll never get great braking in the rear. A weak rear brake is a maintenance issue. Perhaps the lever pivot needs to be disassembled, cleaned, and re-greased. Perhaps the caliper needs rebuilding. Perhaps non-OEM pads were installed or the pads are contaminated. Perhaps the hydraulics are gummed up. The rear brake was excellent for a cruiser when these bikes were new.
Well maybe. I've never got good stopping power with just the rear brake. I have used predominately front brakes for stopping power. I wouldn't say it's a weak brake issue, it's just that the front is much more effective in stopping these heavy bikes. At least that has been my experience. I could be mistaken.