Nova libvirt/kvm sound device

Hi! I'd like to have the following configuration added to every guest on a specific host managed by Nova and libvirt/kvm: <sound model='bla'> <address type='pci' domain='0x0000' bus='0x00' slot='0x1b' function='0x0'/> </sound> When I add the device manually to instance xml, it works as intended but the instance configuration gets overwritten on instance stop/start or hard reboot via Nova. What is the currently supported / proper way to add a virtual sound device without having to modify libvirt or Nova code? I would appreciate any advice. Best regards, Zakhar