windows 8 product ID error with evaluation copy

Question

I've got a toshiba satellite c855d, that came pre-installed with windows 8. I accidentally deleted it when installing Ubuntu. I bought windows 7 (and downloaded the stupid drivers), and now I peacefully dual boot with windows 7 and Ubuntu 13.10. But now, I want to install windows 8 again. I downloaded the evaluation version off of the Microsoft website (100% legal).

I get an error while installing windows 8, at the very beginning, it tells me that the product key entered does not match ... (something something something). I didn't enter a product key! I think windows is reading the product key embedded in my bios, and trying to apply that to the evaluation edition.

I read somewhere that the error was occurring because I'm not in UEFI boot mode when booting my usb. Unfortunately, I have to be in CSM mode because I used WinUSB (in ubuntu) to put the windows install onto my usb. This was the program I used with windows 7, since unetbootin didn't work.

I am currently using unetbootin to put windows 8 onto the usb (from windows 7), and I'll see if that does the trick.

I also tried creating a file called EI.CFG and putting it into the sources folder. This did nothing. I have heard about using PID.txt, but I don't have a product ID.

I basically just need a way to bypass the product key, since I only need to use windows for a couple days (test an application). The 90 day evaluation trial would do fine.