Sadly not; at the end of the day the media component is mainly just layering a nice set of controls (that will look the same across all browsers that allow for customised controls) over the top of the HTML5 <video> and <audio> elements... and the HTML5 <audio> element doesn't include support for a poster attribute.

Two ways you could workaround this:

1. Apply a custom class to that media component that sets a background-image for the component that could mimic poster functionality. You'd need to add some padding-top to the audio element to allow for enough space for the image to display above the audio player bar. You wouldn't get the big play button over the top of the poster image like in the video though; so you might be better off with:
2. Convert the audio to a video that just displays the poster image for the duration of the video.