OTV redundancy with ASR’s

I deployed OTV at a customer site using Nexus 7K’s in one datacenter and ASR routers in the secondary datacenter. I got it all working and then started working on redundancy on the ASR. The downstream switches from the ASR’s are a couple of Nexus 5K’s. I created a port channel on the ASR’s and the 5K’s along with a VPC. I tested communication and all was working well. However when I tried moving the service instance from the physical interface (gi1/1/1) to the port channel the command was invalid.

ASR1000-01(config)# int po2
ASR1000-01(config-if)# service instance 10 ethernet
% Invalid input detected at ‘^’ marker.
ASR1000-01(config-if)# service?      

This stumped me and I couldn’t much info in Cisco’s design guides, the support forum or just searching CCO and the web. I ended up opening a TAC case and was told that was by design. For redundancy I was told to buy a second ASR (which we did from the get go) and create a single leg from ASR-1 to N5K-1 and another from ASR-2 to N5k-2. I don’t like this since Cisco’s datacenter vision is layer 2 and VPC’s.