Actually, there is. If you go into the LiveISO, you can open the terminal and launch manjaro-architect, there is a system rescue there! Would be nice if there was a way to do it with Calamares as well.
You’ll need to create a new partition for /boot/efi, 100MB fat32 should be fine. You can do it with gparted in the LiveISO or use do it Manjaro Architect. You can follow these instructions, but at the end select grub instead of refind.
Alternatively, you can follow these directions 
Let us know if you run into any issues!