How to force Phonegap Build to include a resource during build

I'm building an app with Adobe Phonegap Build. I have one strange issue: my custom fonts work perfectly when testing the app on my device locally, but they do not work when uploading the app to phonegap build. After some research I stumbled upon the following article: http://ift.tt/1tZdUOg

It highlights the problem:

that there was a resources folder “res” created when initializing the environment (not sure if PhoneGap, cordova or Ionic scripts are to blame here). During build, the res contents are not included unless they are specifically referenced in the config.xml file (like the splash screens and icons.)

Now I understand the cause of the problem, but I don't like the proposed solution (move the files to another folder). I don't want to change the structure of my app, I'd rather force phonegap to include those files editing the config.xml file. Nonetheless I wasn't able to find a way to reference the res folder in my config.xml. How can I do it?