I managed to open the enclosure – it’s not too difficult, and it looks undamaged, so I could glue it together again if needed.
Inside there’s basically one interface which is suspected to have UART pins, and probably JTAG pins as well. Yoggie representative on their forum promised to publish the details soon.
The socket is marked as J8, and it’s a 1cm wide, 20-way flat flex cable fixation. It looks like the cable from Farnell.com with the product number AXO-00008 should fit it. Now I need to figure out how to access to the pins of that cable, as it should look rather miniature.