You can run a 4to6 NAT, where specific v6 addresses (the ones you’re talking to) are aliased to reserved v4 addresses out of the PUA.

I have seen people suggesting this before, but it's problematic for a few reasons:

- If you are managing the 4to6 mappings manually, it's obviously not going to be scalable. Just to give people an idea, websites nowadays can connect to 10+ IPs in a single page due to CDN load balancing and stuff.

- If you are handling the mappings automatically, such as by monitoring DNS queries and creating dynamic mappings based on that, the issues become more insidious: applications with hardcoded IP literals would fail without an obvious reason.