Of course it's possible. Take an airplane headlight, mount it on your bike facing backwards, and you're definitely "to visible". :-P

On another note, while daytime riding might be an exception, if they haven't seen you with a 140L, doubling the amount of light output from nearly a single point with a 400L isn't going to make the slightest bit of difference. They're either blind or not looking anywhere near your direction. Wearing a reflective jacket, outlining your bike with lights, etc might help because it makes you bigger and easier to see out of someone's peripheral vision, and a more identifiable shape. But no, I see no point in doubling the amount of light from a small light source without making the light notably wider/bigger.