[libvirt] qemu -net_user features

Hi, I am trying to specify the host name, dns address and some other features provided by qemu -net_user. Right now Im adding a new name space at the end of my xml, like the one below: <qemu:commandline> <qemu:arg value='-net'/> <qemu:arg value='user,hostname=blahblah'/> </qemu:commandline> I am wondering if it is possible to set them within the <interface> name space. My concern is I need to set the host name and dns address using SLiRP for other hypervisors (such as XeN) and it seems they only accept standard libvirt xml tags. Would appreciate if you could give a response on this, and a reason if such thing is not possible. Thanks in advance. Chet