Multicast Over DMVPN
Once you've got your DMVPN up and running, as shown in the DMVPN article, you can enable multicast and PIM.
You just need to know the IP address of your rendezvous point (RP). Then you can roll this out to your hub(s).
ip multicast-routing ! interface Tunnel0 description DMVPN ip pim dr-priority 20 ip pim sparse-mode ! ip pim rp-address 10.16.10.251
The spokes get the same configuration, minus the dr-priority line.