Oh... BTW....

A8 commercial gives full access to all possible shader techniques.

So it may be worth your while to post a 'help' in the shader section.
I suspect it is possible to write a shader that will do this calculation
on the GPU as a form of single-frame object shader...

Im no shader guru, so its out of my league. but if you do post there, I will
keep an eye on the thread in case a guru asks any questions too tricky for you...