how to "discover" the session bus

[Shawn Rutledge]

I'm getting started with libdbus (developing a Scheme binding).

On OpenMoko the issue has come up, how to "discover" the bus address
of the already-running session daemon.  /etc/X11/Xsession starts the
daemon, so inside that X session it is accessible, but what if you ssh
to the phone or otherwise get another shell?  I modified Xsession to
do this

echo "$DBUS_SESSION_BUS_ADDRESS" > /tmp/dbus-session

and /etc/profile to do this

export DBUS_SESSION_BUS_ADDRESS=`cat /tmp/dbus-session`

but was thinking there ought to be a lower-level way to get the
address of the running daemon.

What other mechanisms are there besides environment variables to do this?