You can't, TG.

P8 is still a 32 bit app with an address limitation of 2 gigabytes. Your OS is also 32 bit. Now there are tricks that can enable extended addressing (basically it just forces the OS to use the first gigabyte, then tricks the app into using the next two, but even with tricks 2 gigabytes is the maximum address space you can get out of a 32 bit address bus).

My guess, since this is IDL precalc, is that there is some location(s) in your scene where there is a lot of indirect reflections....possibly even some combination of lighting and geometry that has created an infinite loop. But assuming you opened the task manager and resources windows during this, I would tend to my first guess.