tape device pass-through with virtio-scsi

Environment : RHEL 6.5 with libvirt-0.10.2-29.el6_5.11.x86_64

I want to pass-through a fiberchannel connected tape library device (with 2 tape devices) to a guest, with virtio-scsi driver.

[root]: lsscsi -g
[0:2:0:0] disk IBM ServeRAID M5014 2.13 /dev/sda /dev/sg0
[0:2:1:0] disk IBM ServeRAID M5014 2.13 /dev/sdb /dev/sg1
[5:0:0:0] tape IBM ULT3580-HH6 D2DB /dev/st1 /dev/sg3
[6:0:0:0] tape IBM ULT3580-HH6 D2DB /dev/st0 /dev/sg2
[6:0:0:1] mediumx IBM 3573-TL B.90 /dev/sch0 /dev/sg5

What do I add exactly to the guests xml ?
Or as an alternative, how to configure with virsh ? I find some examples for disks, but not for tapes.

Thanks