I don't see any way through GUI (HDM 15 suite) to move a copy of an existing VD created and saved on another disk into the Backup Capsule. Only seems I can put VDs there by creating a new VD from the Backup/Restore Menu.
It is possible to copy this VD to Backup Capsule using “File Transfer Wizard”. Copy necessary file to clipboard and then to local disk – choose Backup Capsule.