Below is what I wrong before I tested the obvious. Just "import as timeline" the audio only (make sure there is no m2v with the same name); Encore happily builds a disk with black. Mediinfo shows the video stream, but it appears to be at a very low datarate. So, give it a try. I did not burn a disk; just build to a folder and used a software player.
Other options: Encore slideshows have odd problems, I'd play with making a single slide (just black, right?) slideshow, maybe set to manual advance with no advance - or a very long duration to match the audio length.
If an m2v works better for whatever reason, Encore has a minimum bitrate, I think around 2.x or 1.x. So I would try exporting from Premiere,10 seconds of black video using CBR 1.0, 2.0 and 3.0 and see if it matters.