[throw0101a]

AIUI, you encapsulate anything to 2002:192.0.2.4/48 into an IPv4 packet with "41" in the protocol field (as opposed to 6 (TCP) or 17 (UDP)) and send it to 192.0.2.4. 192.0.2.4 would then work as the relay and extract the IPv6 traffic and handle it.

* https://en.wikipedia.org/wiki/IPv4#Protocol

* https://simple.wikipedia.org/wiki/Protocol_41