I've now positioned the bleeper which has to be away from the control box. I decided to place it behind the panel to the right of the rear seat.
This guide shows you how to remove the panels
https://www.a2oc.net/community/index.php?attachments/6cd-changer-fitting-guide-pdf.22137/ but I found I didn't need to remove the panels completely, just the top of the panel.
First remove the Torx screw inside the offside parcel shelf socket.
Then pull back the tailgate seal next to the offside rear light cluster and then pull the panel very hard.
Then pull very hard the panel by the rear offside door seat and once loose then pull up the door seal a bit (the panel has a small clip that engages with the door seal)
In the above photo you can see the main metal clip and it's white housing that holds the panel to the body (not the small clip attached to the door seal). Later I lost the metal clip!
Now I could feed the bleeper up from the light cluster toward the rear quarter light and past the seat belt.
My first idea was to put it behind the panel by the rear passenger seat:
However the self adhesive Velcro I bought on ebay was useless (old stock?), so I abandoned that and for the moment will put it on the quarter light where it is hidden by an A2 Club sticker.
When putting back the panels I had problems. When replacing the panel by the passenger door I was trying to position the metal clip to line up with the slot in the body and the metal clip fell out and fell down inside the panel to the floor level (see red circle in the photo below). By pulling away the panel below it, I was able to get my hand and forearm down and retrieve it. Phew!
Then when replacing the panel by the rear lights I noticed the metal clip was retained in the slot in the body. I took ages to remove it. Eventually I managed to get very long thin nose pliers up behind the clip (shown it red below) and lever the clip up and out. Before reusing it I squeezed it a bit so it wouldn't engage so strongly.
Finally I used a stick glue gun to cover the soldered wires in case they come loose. (see photo in previous post).
Ignore the image below, it already included above.