In virtualbox it is a little bit more difficult to install an OS in a physical disk, but it is possible.
First you need to create a New image normally, but instead of creating a disk image in the computer select Do not add a virtual hard drive.
Then use the VBoxManage to create disk image that point to your external disk (i.e. /dev/sdb) :
# VBoxManage internalcommands createrawvmdk -filename NewHDOS.vmdk -rawdisk /dev/sda
Now just start the virtualbox and click in the Settings -> Storage and add this vmdk file as your hard disk.
Update: Today I tried to do it again and faced an issue: the default Controller was DVD instead “Controller: IDE”. So you need to remove the original Empty device and add again as IDE and then select the .vmdk file to use with it.