One misconception you have is that the front does less braking, it actually does more just like your car. Converting your current bike to hydraulic would be extremely difficult, there are road hydraulic that might be able to be made to work and would work fine with one finger pulling, that's actually the upside of hydraulic but it will be expensive and requiring someone who really knows what there doing to determine if it can be done.
Your other idea is quite common both with tandems which might have it set up with a drag brake and with brake levers for people with can't use one side. Won't take much of a search to find them. Just set the front brake to catch slightly before the rear or youll skid out too much.