All objects in reality reflect from both sides. Corona's not good at fakes, and generally, absence of faking should not prevent getting good result for automotive rendering. Most of specialized automotive renderers are unbiased, so they don't have such toggle, and neither does Corona. I wonder what do you even need refraction pass for.
That being said, what i see on the render looks a lot more like some sort of artifact rather than backside reflection. It looks very weird, in case you mean that bright stripe in middle. Or is that just region render?
If you really need to do such fake (and you should never ever do it) then you can simply plug CoronaFrontBack map into reflection slot, and set front color to white, and black color to black. But it still makes no sense to do such thing, and doublesided reflection should definitely not cause these artifacts. Actually, it's absence of back side reflections what often ruins for example appearance of headlights on cars when using renderers which offer this option.