You will need an IP layer on top of gnu radio to introduce the notion of IP packets. Luckily there is an easy way to do it in linux using tunneling -- i.e. via the dev/tun interface. Read more about it (uncle google knows where information can be found).
As an example, you can look at examples/ofdm/tunnel.py but there's a few things that are missing there. The configuration can be a bit tricky. You will have to configure the tun device and allow for local packets to be delivered with remote IP addresses in the IP header. I forgot how to do this already but there's a setting in the proc file system to do this. Otherwise, the kernel will drop such packets.
Also, do not expect ICMP to work.