I just saw something on YouTube that might completely solve the bridge problem .
A guy at Norman's Rare Guitars was reviewing an early 80's Gibson Ripper bass with what looked like a standard three point bridge, but instead of the strings terminating at the bridge they come out the back side and go through the body. Since the ESB-4 has a solid center, this should work on it as well.
I took a look at the bridge that came with my ESB-4 kit and I think this could work without modifying the bridge. All you would need to do is drill four holes and install some Fender bass sting ferrules.
I am ok now with the trapeze system I came up with, but is am sure I'd have tried this if I had seen it in time!