Not sure on which part of the ESC is the voltage protection actually protecting. You can try it with a BEC but I don't think you will get far. Even if you manage to make it work I doubt it will last all that long if at all.

Maybe you should do some lipo surgery and remove couple of cells to make them into a 6S pack since you already have so many of them. Other than that your choices are limited IMO.

You could also get your self a HV plane/heli esc and a Pistix controller. That will work in your Redcat easily but you will have to say goodbye to reverse and figure out how to run mechanical brakes.

Also partially charging the pack to total voltage just under 30V will not work neither with the HW ESC. As soon as you hit the brakes that voltage will spike well above 30V and cook your ESC for sure. I really wouldn't attempt it.