libvirt users - Jul 2015 - How to enable vmx (virtual machine extensions) in virt-manager

I need to enable virtual machine extensions, like as described at
http://www.server-world.info/en/note?os=Ubuntu_14.04&p=kvm&f=8 . I could
do this in virsh, but I'd like to know if it's possible to do in
virt-manager.  I don't see an obvious way to do that.