Currently there is no way to selectively raytrace, but I agree it would be a very useful feature. I think there could be some additional tuning here though that would maintain reasonable render times and still increase quality. Generally speaking don't worry about that, it's something I'll have to tackle if your entry ends up winning.
By the way the frame blended version really does look much better, quite good in fact. What app are you doing the blending in?
- Oshyan