Hello. I am not sure I have the full picture here. Are you saying that you have two links between the IPN devices (I assume a pair of IPN devices in each pod) and you only want traffic to flow over one of them, and if it fails, use the other link? Ideally, you would have both links active, and either create a full-mesh between your IPN devices, or make an extra link(s) between local IPN routers and change the OSPF costs to ensure that the path to your PIM BiDir RP does NOT go through the spines. The spines don't speak PIM and will drop any packets (bad news and breaks your MPOD setup). It should look like one of these two pictures.
You also definitely want to read the design guide here because beyond possibly adjusting OSPF metrics, you will also likely want to use the 'Phantom RP' approach too.
Hope that helps!