You can't do it for the simple fact that this is a one way connection and the AE-based MOGRT container has no knowledge of your premiere audio tracks. Not that it would matter much - since AE can only do basic stereo and no multichannel stuff, the whole concept would fall apart, anyway, as soon as you add more than towo mono tracks or a stereo track. You'd have no way of accessing other channels. Since Premiere doesn't have something liek expressions, I think you can't do it there, either. The best thing I can think of is that you may be able to creatively use a Premiere plug-in that e.g renders a faux "video camera seeker" overlay. Some of them feature audio indicators and may be able to automatically detect which track is currently active. But that's really more of a premiere question, so ask on their forum.