libvirt users - Jan 2012 - possible to disable but not remove hardware?

I have a situation where I frequently need to "add" and
"remove" a NIC,
but each time I "add" it, I need the same MAC address.  I'm using 
virt-manager mostly, but would be willing to use "virsh" if necessary,
although it doesn't seem to hotplug the same way (something else to 
figure out another day ;-).

It doesn't appear in the domain XML format that there is any
"disabled"
attribute than can be used.  Is that true?  Is there a different usage 
pattern to accomplish this?

Thanks,
David Mansfield
Cobite, INC.