AC3 Passthrough for Plex

I wish there was an option for the ATV 2’s Plex client to request a video with AC3 passthrough from the server. As it stands now, the audio stream is automatically transcoded to what appears to be AAC 2.0.

What is so frustrating about this, this should be a trivial flag setting, but no programmes seem to care about AC3 preservation. XBMC is broken, AirVideo does not do it, Plex has no server side settings for this, etc.

Please, somebody help.