Not quite so. On T520 the flash chip is accessible right after you remove the keyboard and the palmrest and there's no need to remove the motherboard from chassis.
Sorry, my bad. I mixed up my facts there.
Although it's possible to use just the 8M chip by using modified layout, it might be confusing for a beginner.
I managed to flash my T430's both flash chips by splitting the 12M coreboot image into two parts (4M + 8M) and flashing the chips separately, is this not a good option? This way I don't have to pass a layout file to flashrom, it just writes to both chips. It also allows me to have a larger CBFS.