I would just try. Setup a new 'api' environment for api.example.com and then try to query a route that shouldn't work with it.

So, for the future googlers out there, here is what I ended up doing. I add a "sub" environment to my environment detection for configurations. So, now, I have environment detection based on machine name AND beneath that site detection based on subdoman (or root). My configs now cascade:

app/config/environment/site/file.php app/config/environment/file.php app/config/file.php

or

app/config/local/api/app.php app/config/local/app.php app/config/app.php (production)

This allows me to load specific configurations (including Facades and Service Providers) for my subdomains while maintaining different environments.

Here how I did it (I haven't tested this for security vulnerabilities on production yet, but its pretty simple):

Step One: Modify Environment Detection
In my bootstrap/start.php, I edited $app->detectEnvironment like so

$env = $app->detectEnvironment(	function () use ($app) {
    
    // First, we find the environment
    $hosts = array(
	'dev' => array('DarkeMedia'),
	'staging' => array('SomethingElse'),
    );

    $args = isset($_SERVER['argv']) ? $_SERVER['argv'] : null;

    $environment = $app['env'] = with(new Illuminate\Foundation\EnvironmentDetector())->detect($hosts, $args);

    // Now, discover the subdomain site
    $http_pieces = explode(".", $app->request->server('HTTP_HOST') );
    
    $GLOBALS['site'] = ( count($http_pieces) > 2 ) ? array_shift($http_pieces) : 'root';

    return $environment;
});

Step Two: Extend the FileLoader to cascade the extra level
First, created my own Application class that extended Illuminate\Foundation\Application.
Next, I instantiated my application in bootstrap/start.php.

//$app = new Illuminate\Foundation\Application;

$app = new Director\Application;

In my Application, I overloaded the getConfigLoader() method. This method is responsible for return an instance of the Config File Loader. This loader is what actually finds and loads the config files. I wanted to adapt this to search another layer deeper. In order to accomplish this without editing core, I simply extended FileLoader and told Laravel to use mine instead.

namespace Director;
use Illuminate\Filesystem\Filesystem;
use Illuminate\Foundation\Application as LaravelApp;

Class Application extends LaravelApp\{  
    
    /*
     * Overload the Config Loader
     */
    public function getConfigLoader()
    {
            // This FileLoader is under my namespace (Director\FileLoader)
	    return new FileLoader(new Filesystem, $this['path'].'/config');
    }

Step Three: Adapt the FileLoader
Now, I created the FileLoader Class that extends \Illuminate\Config\FileLoader

namespace Director;
use \Illuminate\Config\FileLoader;

Class FileLoader extends FileLoader{  
    
    /*
     * Overload the Config Loader
     */
	public function load($environment, $group, $namespace = null)
	{
	    // Call the parent, so it looks in all the normal place
		$items = parent::load($environment,$group,$namespace);
		
		// Now look for one more level of cascade based on the global $site we created in bootstrap/start.php
                $path = $this->getPath($namespace);
		$site = $GLOBALS['site'];
		
		$file = "{$path}/{$environment}/{$site}/{$group}.php";

		if (file_exists($file))
		{
			$items = $this->mergeEnvironment($items, $file);
		}

		return $items;
	}

It may not be the most elegant solution, but it worked for me. Interested to know how I could clean this up!