Using Spotify on Zombies 5K

I got Zombies 5K some time ago through a Humble Bundle but I noticed that I can't use a Spotify playlist while playing it / running. While the free version of Zombies! Run! has support for external playlists, Zombies 5K doesn't (and it's a paid version). Since I have almost no locally stored music on my device I was wondering if it's in any way possible to use a Spotify playlist since running in almost complete silence is quite boring.

Zombies, Run 5k does not support using a cloud service (Spotify, Google Play Music) to play music in the app.

In order to play music in this app you need to create a play list with local music by plugging your phone into the computer and copying some music files to it.