I spoke with Brightcove and they did say it is possible to force one rendition through the API.
“Alternatively, if you prefer to enforce which one of the renditions must to be played, you can do this through the Player API calls. We have an article showing you how to achieve this: Selecting Dynamic Delivery Renditions: http://support.brightcove.com/en/video-cloud/docs/selecting-multi-bitrate-streaming-renditions”
