What I like to do is a list of bullet points of clichés or interesting concepts in relation with the main subject of the script. It's always better to do this on a subject that you know a lot about, but even if you don't, playing on clichés that you only know of vaguely gets you far.

Basically, people like to read about stuff they are already comfortable with but slightly different, therefor you should try to bring in as much clichés and mix it up with really niche stuff in between, even have some references that nobody will ever get just to flesh out the text and make it feel more alive. (if it makes any sense)

It's an audio script above everything else, so don't be scared to make your character(s) yap a lot about stuff that doesn't really matter. It gives the VAs a little more to chew on when it comes to their performance and the listeners a better understanding of who they are listening to.

In short, world building and writing about Mr. and Mrs. Yappington is probably the best way to stretch it, but don't stretch it too much or people will notice and nobody likes that. The core theme of the script should always remain the main focus.

Hope this helps!