TL;DR - Audiobus has midi support, use MIDI Tools to transpose.
Slightly longer explanation:
Note: This was tested with
First, get ahold of Audiobus 3 if you don't have it. It has an ability to use AUv3 plugins and, for a nominal fee, it will allow you to work with midi signals as well.
Once you have Audiobus 3, go into the MIDI section (button on the lower left). There will be three boxes. The far left is inputs, the far right is outputs, the middle is for "Midi Filters".
Assuming your Lightpad is off, to hook it up do the following:
Secondly, you're going to need to route this to Virtual MIDI. So: