Aye, doing it all in post is fun but it will never give you the correct optics... One way to do it, and Vile may have written a Tutorial on it, I'm not sure, is to make an actual Lens. Take a two spheres, intersect them with Boolean grouping, and you have a "real" fake lens. Track it to the camera and position it, and set it's material to a glassy one. Now you can control the amount of wash in the image with the Material Lab in Bryce, and it will look much more realistic. Haven't done any lightning, yet, but you could theoretically pull it off with volumetrics. This lens example is a great way to keep it all in Bryce, remember, lense flare is something camera photographers are trying to avoid, the fact that we work TOWARDS it speaks volumes about our idiocy.