setkey and -ctx

[Zaphod Beeblebrox]

I have a Cisco ASA which expects a different tunnel for each IP that
I'm sending traffic to (ie: it expects a different tunnel per firewall
rule over there).  It looks like I should have each SA in a different
domain on my side to do this --- so it looks like I should be using
the "-ctx" flag to setkey (or in /etc/ipsec.conf).  But setkey appears
to reject this...

Is this unimplemented?  Am I missing something?