Hi Ben,
I wanted to add the dot buttons as well, so I did some tweaking myself a few weeks ago and got it working. Wanted to finish it up today and came across your comment, so I decided to upload it.
You can find it here: ZHA - Ikea Symfonisk sound controller GEN2 (the square one) with dot-button support for new firmware.
Should have full control for the two dot-buttons with options for single, double and long press. You do need the newer firmware, but I also link to a resource on how to update if necessary.
Hope this helps!