rEFInd can auto-detect bootable devices, and you can select them during startup. You need to install it to the efi partition as your boot manager.
With a simple config edit and file copy operation, I put a memtest86 efi image on my boot partition, and it shows up as an option for every boot. It's nice to know I won't have to fumble around with USB drives if I need to test my RAM in the future.