System D-BUS and $DISPLAY

Hi,

Is there any "good" current solution for telling a GUI application
activated through the system D-BUS which $DISPLAY it should use?

There was recently a discussion[1] on the bluez-devel mailing list about
how this should be handled with the bluetooth pin-code dialog. The
conclusion was that the best way currently is not to use activation at
all, but to have the application running all the time in the background.

I can think of a couple of possible solutions to the problem, but it
would be interesting to hear the opinions of D-BUS developers on this
issue:

1. Have some well known D-BUS service started by X which can answer the
question "which display should I use?" for activated applications.

2. Have some method for X to tell the D-BUS daemon a default $DISPLAY
while the daemon is running. Before activating services the daemon
would then set the DISPLAY variable accordingly.

3. Don't use activation with system D-BUS (at least not for GUI apps)

br,
Johan

[1] http://sourceforge.net/mailarchive/forum.php?thread_id=4946573&forum_id=1881