Mapping passive elements (LEDs etc.)


I’m playing with mapping Ipad Midi Studio to djay for Mac. everything seems to be ok but I have a question:

For example, if I want to show current deck volume on led volume indicator (it is not real led in my case, but the approach will work in other cases) and I know it’s midi address, how can I access it (it produces no actions, so I can’t catch it in midi learning window) and what action should I map to it?

Thank you in advance