Easy2Boot can support multiple UEFI payloads by converting each one into a .imgPTN file.
If you have already have your two working USB flash drives, just install the MPI Tool kit from the E2B site and then drag-and-drop the USB flash drive Explorer icon (e.g. for U

onto the MPI_FAT32 Desktop icon - this will make a .imgPTN file. Then copy it to your E2B USB drive (e.g. \_ISO\MAINMENU folder). Repeat for the other flash drive. (alternatively, drag-and-drop the ISO or zip file onto the MPI_FAT32 Desktop shortcut).
Now you need to 'switch-in' the partition image before you can UEFI-boot from it. There are various ways you can do this:
1. Run \_ISO\SWITCH_E2B.exe and double-click on the .imgPTN file
2. MBR-boot from a BIOS system (or a system with CSM mode enabled) and boot to the E2B Main menu - then select the required .imgPTN file.
3. Run \QEMU_MENU_TEST.cmd to run a small emulator and boot to the E2B Main menu and select the required .imgPTN file.
Once you have switched in the .imgPTN partition image, you can now UEFI-boot from the E2B drive.
To switch it back to 'E2B mode' run \e2b\SWITCH_E2B.exe - Restore E2B Partition(s), or boot it on a BIOS/CSM system to the CSM Menu and choose option 0.
There are several YouTube videos showing you how to do this.
Adding UEFI (.imgPTN) images :: Easy2Boot