[CentOS-virt] change network settings of VM depending on logged in user(s)?

Hi,

is there a way to disable internet access for a windoze 7 VM depending
on which user(s) is/are logged in?

It seems windoze 7 doesn´t really support this, especially when you want
to disable internet access for the whole machine, so I´m wondering if
there is a way to do this when the machine is a KVM-VM running on Centos.

The whole VM should only have internet access when a particular user logs
in, and preferably for only this particular user.