Requirements

1. USB Overdrive
2. A non-Apple keyboard with media keys (or keys you want to make "media" keys). For reference, I'm using a Microsoft Sidewinder X4

Set Up

1. Plug in your keyboard and install USB Overdrive.
2. Open USB Overdrive. Click into the Settings tab.
3. Click the dropdown and select "Any Keyboard, Any Application"
4. Click the "Scan Next Track" item in the left-hand list. You can also select this key by focusing the USB Overdrive window and pressing the actual key on the keyboard.
5. In the right-hand column click the dropdown and select "Execute AppleScript".
6. Paste the following AppleScript:

   tell application "Spotify"
   next track
   end tell
   

7. Repeat steps 4 and 5 but select "Scan Previous Track". Paste the following AppleScript:

   tell application "Spotify"
   previous track
   end tell
   

8. Repeat steps 4 and 5 but select "Play/Pause". Paste the following AppleScript:

    tell application "Spotify"
       playpause
    end tell