RCRuiz has posted a hack that speeds up Photon Map rendering in Yafray a great deal. It's a bit thin on the details but it would seem that he stores the photon distribution in your scene so that you can quickly re-render it from any camera angle and position.
As long as you don't move any objects or lights this should work fine. For many types of fly-through animation, such as architectural walkthroughs, this will be a great timesaver.
The downloads and instructions can be found on Elysiun.