[libvirt] libvirtd and LVM snapshots

I'm working on an existing system that creates, manages, and destroys Xen guests on a pool of host systems, and I use LVM copy-on-write snapshots to keep creation rapid. http://libvirt.org/storage.html describes logical volume pools, for which you simply supply the name of a volume group and it allocates volumes from that. By my reading, it appears one can even provide a list of block devices and they will be carved into extents and pooled into a VG for you. Is there any interface to libvirtd that allows it to create volumes that are snapshots of existing volumes? If not, does anyone have advice for doing so manually in a way that plays smoothly with libvirt? -- Support your droogs! Nick Moffitt nick(a)zork.net