You can add an unlimited number of fully installed linux OS's to an E2B drive (if you have enough space!).
Each OS image will be fully functional and all changes will be persistent (i.e. not just live+persistence mode but a full OS).
You will need a Windows system to prepare the images (two .imgPTN files per OS).
You will need to use Virtual Box and VMUB to install the linux OS.
The linux distro must be able to be fully installed onto a single partition as root (\).
Prepare two image files, one for the grub4dos boot files, one large, ext3/4 one for the linux partition using Make_Ext.exe or RMPrepUSB
Switch to the new partitions by booting to E2B and selecting the .imgPTN file
MBR-boot from the linux ISO file using Virtual Box and VMUB and format+install to the empty large partition on the E2B USB drive
Tip: Do NOT allow it to delete or create new partitions. You should only format the sdx3 partition.
Now you can MBR-boot on any system to the full linux OS!
Here is one method for Kali which is applicable to most Linux distros.
Note: Do NOT allow the installer to create or delete existing partitions because the drive will probably not be bootable afterwards! Just keep the same file system type and use the format option only. Use Make_Ext.exe to create the correct file system (e.g. ext3 or ext4) first.
For a detailed description of more linux full installations, see the blog Tutorials list (search for 'full').
It may also be possible to add a swap file if the Linux OS supports one.
Note that you may have problems if you attempt to update Linux to a later revision if the boot files are changed however, so take a backup of the .imgPTN file before attempting a version update