Such a setup is not supported by Microsoft. Unless you find some hack on the web, you need to do this the supported (EXPENSIVE) way by installing 7 clean and maybe by setting to UEFI to legacy mode (BIOS) and then installing 7 clean. Then leave unpartitioned space to install your second license OEM Windows 8 Pro to .
The license of Windows 8 is forgotten and some folk get uppity about this.
You can install Windows 7 Pro or better in a virtual PC like "Virtual Box" if need be.
I want to install W7 on my newly acquired notebook with W8. So, for that I download W7 and burned it from ISO to a DVD and put in the notebook. Now, I am not an expert, but still didnt want to spend money on pc technicians, so I was careful about looking for information on how to reboot (I selected UEFI configuration on advanced options). After going into BIOS, I set the order to 1st boot device CD/DVD, and 2nd boot device hard-drive, and put Secure boot to disabled option. So, when I restart windows and it asks to press a button I do it and then it shows me a long message, which says:
"Windows failed to start. A recent hardware or software change might be the cause. To fix the problem:
1. Insert your Windows installation disc and restart your computer
2. Choose your language settings and then click "Next"
3. Click "Repair your computer"
If you do not have this disc, contact your system administrator or computer manufacturer for assitance.
Info: An error ocurred while attempting to read the boot configuration data.
I hope you can help me solve this because I have no idea to do, and as I said, I am not an expert. I dont know if the problem is the CD or the Windows itself.