Secure UEFI + MBR boot almost any file (a1ive's grub2 File Manager)
A1ive has enhanced grub2 functionality to add the partnew command + other commands.
Try the new .imgPTN file which has a1ives new File Manger.
Just copy your ISO files, .VHDs, .WIMs, .IMG files to the second NTFS partition on your E2B drive and boot directly from them.
I have added a special UEFI-patched boot file which should UEFI64 Secure Boot and allow you to run signed or unsigned boot files.
You can also add you own menus by adding .grubfm files (e.g. Ubuntu + persistence). See my blog articles for details.
Note: Some systems will refuse to allow you to MBR-boot if they contain EFI boot files. There is no workaround for this - if you want to MBR-boot on these buggy systems, you can rename the \EFI folder on the FAT32 partition.