How to create new boot files in external HDD?

Hi. I am aware I can select a BCD file from a different HDD than the master boot in use. So I removed an HDD from an ultrabook and attached into my PC by SATA. However, this HDD got nothing in the first partition (boot partition), it was cleaned up accidentally, so I can't select the disk to work on it. I was thinking if there is some "scrap" image of what suppose to be in this partition so I can edit it...

I did remove the HDD because this ultrabook got no optical disk an the UEFI boot usb flash drive won't boot. I can only boot by legacy system but than I can't change HDD content that is in UEFI - something like that.

Anyway, I think will be nice to be able to recreate boot files/partition of an external HDD, don't you think?