NAT46, translate with v4 embedded in source

Good day,

I've been playing with setting up 7.1 as a NAT64 gateway so I can have v6-only hosts on my LAN and still reach the v4 internet, and that's been working great.

I'm now trying to handle the opposite (NAT46), so external v4-only hosts can reach my v6-only servers. I'm able to get the packets delivered, but the translated source address is "squashed" to a single IP and I'd like it to contain the embedded v4 src address.

Example setup:

External client IPv4: 203.0.113.4
My public IPv4: 198.51.100.4
My internal IPv6: 2001:0db8::6
My internal NAT64 prefix: 2001:0db8:6464::/96

Client contacts my public IPv4:

203.0.113.4 -> 198.51.100.4

I want PF to translate the packet so the IPv4 source is embedded in the translated source:

2001:0db8:6464::cb00:7104 -> 2001:0db8::6

The closest I've gotten is:

pass in on $wan inet to 198.51.100.4 af-to inet6 from 2001:0db8:6464::/96 to 2001:0db8::6

The packets are delivered and translated, but the source address gets squashed to the literal "2001:0db8:6464::". I'd want the client's "203.0.113.4" put over the low-order bits of the source address as "cb00:7104".

Essentially, I want stateless NAT46. I realize PF is always stateful and thus doesn't *need* to embed the source to track the packets, but in this case having it would let me run log analysis on the host without having to consult the firewall.

I've been over the options in PF but can't find anything that will allow me to specify that the SOURCE address have a v4 embedded in it.

Am I missing anything?

Thanks,

Jason