Yes that works. Copy EFI partition from MemTest86 USB media to new additional partition on top of bananapi_bpi-r64-sdcard.img
. Then also store dtb next to BOOTAA64.efi
inside that FAT partition.
In U-Boot shell:
fatload mmc 1:X 0x40080000 EFI/BOOT/BOOTAA64.efi
fatload mmc 1:X 0x40090000 EFI/BOOT/BPI-R64.dtb
bootefi 0x40090000 0x40080000