You can launch the installation using virt-install or raw qemu-system-x86_64 commands.
# Offline qemu-img snapshot -a before_patches windows7.qcow2 windows 7qcow2
Since Windows 7 is unpatched for new vulnerabilities: You can launch the installation using virt-install or
qemu-img create -f qcow2 win7.qcow2 40G