Centos 7.x USB Install Media (Add Centos to Multiboot)

As it used to be cool, you take the CentOS 6.x image, pull pieces out of it, and shove it all onto a USB flash drive, next to other systems.

But, starting with Centos 7, it became a bit more difficult to do this, and the only official way was to record the image directly on the media (with the loss of everything that already exists on it).
But, having applied a little ingenuity, I could solve this problem, I ask under the cat:

I think it will work for everyone to pick out the files from the image (mount the image on a loop or you can open it with 7-zip). Next you need to drop the files on our flash drive (you need to put something in the root, you can cut out a section for this, as it is convenient to whom).

Further, a little magic of the kernel command line parameters (look in /isolinux/isolinux.cfg):

label linux menu label ^Install CentOS 7 kernel vmlinuz append initrd=initrd.img inst.stage2=hd:LABEL=CentOS\x207\x20x86_64 quiet 

The most interesting parameter for us is: inst.stage2 = hd: LABEL = CentOS \ x207 \ x20x86_64
It tells boot scripts and installers where to look for packages and other files that are needed for installation. Here is a link to the section labeled "CentOS 7 x86_64".
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Then everything is simple, add to the boot menu of our CentOS flash drive, and prescribe the label of the section on which the files from the image were thrown.

That's all, just consider the used FS on the flash drive, the installation image (its core), should be familiar with this FS.