I am not sure, but as far as I remember, there was an option to install it on the mSata drive (used as cache), but you need to disable it's usage as cache in bios (intel smart response). WARNING! Probably you will loose all info on both drives if you install something on any of them.
With my notebook, I replaced 500Gb hdd with 256 Mb Intel SSD and installed Windows there. And I use mSata cache (32 Gb in my model) as a second drive. 500 Gb hdd put in the hdd box and use it as external storage.
As for my initial problem (with serial number), I was able to solve it.
Just use notepad to make a file called PID.txt and put the following in the file:
[PID]
Value=XXXXX-XXXXX-XXXXX-XXXXX-XXXXX
Place your windows 8 Pro key in where the X's are and save the file to the /sources directory in the root of your USB key.
The PID file overrides the pre-installed OEM key in the bios of your computer. Windows 8 installation starts right up.