EFI_NOT_FOUND when attempting to boot Windows 7 from ESP on another drive

[halian]

Per topic, I get OpenSubvol returned EFI_NOT_FOUND when attempting to boot Windows 7 by reference to the btrfs UUID when the EFI System Partition is on another drive. Is there a way to fix this, and if so how?

I initially thought it would be necessary to pass the subvolume number as an argument, but when I do so, I get the following errors:

ARC name is btrfs(xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx).
Could not open Windows on volume.
Open returned EFI_NOT_FOUND
boot returned EFI_NOT_FOUND