Abstract question time!

I'm trying to create 5 main menu backgrounds (a1-a5) to replace the standard menu backgrounds that come with Portal 2. The backgrounds will change, but only based off of the stock portal 2 maps. For example, if the background is currently playing the A2 video, and you play one of my new A1 maps it will not change. However, if you play one of Portal 2's A1 maps, the background will change to the correct one (the A1 background video).

Any ideas of how to get the game to recognize my maps, and change the background videos based on the playing of my maps as well?

Thanks for the help!

The name of your map has to start with sp_a?_ to be recognized, but I assume you already know that.
If the map is installed through the Workshop, however, there's a directory name in front of the map name, which prevents this from working. The BSPs need to be placed in manually.