Ray differentials (or other texture tricks) for glossy reflections?

[CraigMcN]

Hi,

I'm playing with glossy reflections and wondering about good ways to
sample textures (and specifically environment maps) when seen in
glossy reflections. For environment maps I can use multiple
importance sampling for when the map is seen directly in a glossy
reflection (which works pretty well), but when the glossy object sees
another perfectly specular object which then sees the environment map
you've got no guide as to how to sample those directions, and the ray
differentials don't reflect the "spread" of the glossy reflected
rays. The end result is that high contrast environment maps turn into
speckly nonsense after a second bounce and require an enormous number
of samples to get good results.

Anyone have any ideas on good ways to deal with this situation?

Cheers,

Craig.