Double NAT, but one is 1:1

I’m in a somewhat odd situation: my home router and my ISP both do NAT, but my ISP does 1:1 NAT. I’d like ipfs to be able to determine my external address and announce that instead of my ISP-internal (my home router does NAT-PMP, so that’s not a problem). At this point, I’d be happy just having a way to override the IP address (but not the port) that it announces, but in the long run, it would be nice to have a way for ipfs to do this automatically. For example, we could have a config option that tells it to determine its external address by talking to peers and then announce that.

Is there a way to override the IP address without also specifying the port?