multicast senders behind an IGMP Proxy

During WGLC, there was clear consensus from MAGMA and MBONED that supporting
multicast senders behind the IGMP Proxy device was desirable.  However,
while wrapping up draft-ietf-behave-multicast-07, Toerless pointed out a
problem with multicast senders behind an IGMP Proxy device (any IGMP Proxy
device -- not just an IGMP Proxy in a NAT).

The problem is that any multicast flows generated behind the IGMP proxy will
be forwarded up the access link towards the Internet -- even for flows that
you want to keep within your network.  Concrete examples of generating
multicast within a home network include:

 * sending audio to all of your IP-enabled speakers distributed 
   throughout your house,  
 * IP-enabled intercom system, 
 * HD video to multiple telvision sets (kitchen and living room).

In each case, you "could" do unicast, but especially for HD one might easily
envision not having sufficient bandwidth or not wanting to waste the
bandwidth (which might be used for other things).

Does anyone have suggestions on how this might be resolved?

-d