Comment 4 for bug 396219

If you are using libvirt
create /etc/libvirt/qemu/kvm-32
-------------------snip-----------
#!/bin/bash
exec kvm -cpu qemu32,-nx `echo $*`
---------------end-----------------
use qemu64 for 64bit.

Then modify domains to use the wrapper script
virsh edit <domain>
change emulator in device section to:
<emulator>/etc/libvirt/qemu/kvm-32</emulator>

It may be a good idea to ship with a wrapper and a config file to pass extra options to kvm
from libvirt, since it's not easy to pass them now.