Lessons learned:
1) see title of question/comment;
2)do NOT create a static group, because this REGISTERS it;
3) spoof the sender as mrouter through VLAN configuration;
4) change the default handling of unregistered multicast from flood to send-to-mrouter (or whatever it is)
5) send queries from sender
6) respond with join/report or leave from receiver
At least under whatever remaining variables exist in my experiment, this does succeed in filtering what is seen on a receiver tcpdump. None of this is intuitively obvious.