I found the email from may 2005 which had the man page of rtcontrib and this statement from Greg Ward:
"Rtcontrib can also be used by the more adventurous among you to
compute input/output relations for devices such as light pipes and
shading systems, although I have yet to test such an approach,
I would like to try this for an anidolic system of mirrors (set of parabolic mirrors, thus cannot be accurately modeled with direct sun), but I have not yet figured out from the man page quite how to do this.
I wonder if anyone else has attempted something similar and would be willing to tell me about it, or if Greg has experimented with it.
Thanks for any help,
p.s. If I manage this, I will also be attempting to use Daysim to do a daylight autonomy... if anyone can see any potential problems with this, please let me know.