Enter your UEFI menu, select "Boot maintenance manager", then "Boot options", then "Add boot option", then "NO VOLUME LABEL,....Primary,Slave...1, GPT,..", then browse the /EFI/ubuntu/ folder via the UEFI boot menu, and select the grubx64.efi . Give it the name you want (eg "Precise"), then "Commit Changes and exit", then Enter.
And to remove entries as UEFI remembers them.
UEFI system only shows ubuntu. Delete ubuntu entry & reboot a couple of times & it resets to defaults including drives & USB ports.