The problem is the MBONE doesn't reach the target audience.
If just multicast access is the problem, then why not use a number of
multicast/unicast reflectors as was done on the last SIGCOMM conference.
One application for this might be the marratech Session Proxy which can
be found on e.g.
www.emeetingportal.com or
msp.cdt.luth.se:7000
All you you need on the receiver side is a way to launch mbone tools via
a SDP-file delivered via HTTP (like e.g. the free Marratech Player or
the commercial Marratech Pro) or be able to launch the tools manually.
/P