VM interface mac address persistent

using virtio-net with ubuntu 10.04 kernel 2.6.35.
I want change the interface mac temporarily and hope it return to original mac after reboot. Currently we can only achieve that by shutdown the VM and restart, but if just reboot it will persistent to use the temp mac we just changed to.
It doesn’t matter if I specific mac or not when create the VM, it is same behavior. Any Idea?