Mount a VirtualBox disk image:

VBoxManage internalcommands dumphdinfo [NameOfImage].vdi

- Find the data offset (offData) parameter

use losetup to make a loop device at that offset + the offset to the partition you want (32256 for the first one)

Note: if copying a virtual partition out onto a real one,
double-check for off-by-one errors in the offset by making sure that
the first sector looks correct early in the copy.