Install Windows 7 on iMac 11,3 (late 2010 model) without Boot Camp or OSX?

I have the following setup:

iMac 11,3 (late 2010 model).

Sole OS is Ubuntu 14.04 LTS.

The last installed OSX version was 10.8 (I still have this on an external HDD from which I boot the machine from time to time).

I would like to install Windows 7 on this machine as a dual boot with Ubuntu. I have partitioned the internal HDD to make a new NTFS partition.

I then proceed to boot the iMac from a Windows 7 64bit install DVD but the boot loader does not see the DVD.

I also tried the refind boot loader and that too does not see the DVD.

When I try to boot from the DVD the disk drive seems to by trying to read the DVD and then spits it out after a few seconds.

I have also tried making a bootable Windows 7 install USB (I tried creating this USB both from within Ubuntu 14.04 using UNETBOOTIN and from within OSX 10.8 using Boot Camp).

Depending on which method I used to make the USB, in some cases the iMac boot loader sees "EFI Boot" and when I select that it simply hangs. In other cases the boot loader will show me some boot options from the USB but then I either get a "Bootmgr is missing" message or I see a black screen with a white blinking cursor and nothing else happens no matter how long I wait.

How hard can it be to install Windows 7 on this iMac? What am I missing/doing wrong?

It seems the only way to install Windows 7 would be to have OSX installed on this machine with only 1 partition and then to go through Boot Camp.

This seems awfully restrictive unless I am missing something?

Anything else I can do/try? Or am I doing something wrong?