You most certainly can. All you need to do is when you declare your assets at the top of script.js, you'll just declare them like this.
monogatari.assets ('voice', {
'<voice_id>': 'chapter1/voiceFileName'
});
Additionally, if you wanted to point your files to completely different location, like a different server maybe, you can do that by going into options.js There you'll find a list of default locations, such as the voice folder points to assets/voices. You can change that to whatever you want. For the example you asked, though, you won't need to do this, just letting you know how it works. Basically, the URL to the file is the string found in options.js plus the string you provide in your asset declaration.