SQL Server 2014 Always On .. can I have replication without a listener?
You can configure multiple listeners but what I think you want to do is just configure the other IP (for the 3rd replica) at the cluster level so that your AG resource can access it. If your cluster is configured for the multi-subnet then you should have the ability to add the IP for that 3rd replica to your current listener. 

If I recall you might have to create the role in the WSFC for your listener as a client access point. I know this is the required configuration when I have built AGs in Azure environments, but those may be special circumstances compared to dealing with all on-premise setups.