Lightroom MIDI plugin
http://knobroom.com/
Work in progress
File -> Plugin Manager -> Add, select Knobroom.lrplugin and click Add Plug-in.
In the mapping section, import MIDI mapping for your device (some expertise required here).
Click Done from Plugin-Manager.
File -> Plugin Extras -> Knobroom -> Start Knobroom.
You should see device selection dialog with MIDI In and MIDI Out devices listed. Select your device and click Start.
Knobroom should now be operating, when you move sliders from Lightroom, it sends MIDI out messages to selected MIDI out port, based on the mappings set in preferences. Similarly, when MIDI in message is received from device, it is mapped to Lightroom develop setting and applied on the current photo history.