multiboot

1. Set up according to the instructions here.
2. Clone this reop onto a separate ext4 partition locally.

git init .
git remote add origin https://github.com/hongyi-zhao/multiboot.git 
git pull origin master
git branch --set-upstream-to=origin/master master

3. Then use this repository with my revised version of multibootusb on the same local partition:

git clone https://github.com/hongyi-zhao/multibootusb.git multibootusb.git

Some more advanced usages:

http://www.dolda2000.com/~fredrik/doc/grub2
https://unix.stackexchange.com/questions/253657/actual-usage-of-grub-mkimage-config
http://lukeluo.blogspot.com/2013/06/grub-how-to-4-memdisk-and-loopback.html