it is true that you cannot run the kernel without an initramfs.
So you need to have an initramfs. But where can you get one?
The easiest method is to use the initramfs of the Amazon kernel as a template. Normally no modifcations to the Amazon initramfs are necessary, so you will just have to repack that initramfs. The resulting cpio archive can be used as input CONFIG_INITRAMFS_SOURCE.
I have updated the compilation post
in order to reflect this.
There are also new detailed instructions available on how the initramfs can be extracted from the Amazon kernel. I added this information this post: http://www.christian-hoff.com/?p=16
Hope this helps!
And I wish you good luck with your compilation attempts.