I have noticed several people listing transformers with yellowed plastic in the show your haul thread and thought I would pass on this link that I found! I have not been able to try this myself yet but if it doesn't damage the plastic in the long term this is pretty damn sweet!
This is that link I always keep referring to and not finding...
We do have this in our tutorial section I think (Yup, post 16: http://www.cybertron.ca/boards/showt...?t=5671&page=2), and there is definitely a thread where we have been posting our own results and generally discussion.