Adding a method to vendor class

I'm using the laravel-elfinder package (https://github.com/barryvdh/laravel-elfinder).

My aim is to automatically resize and copy any uploaded images so I can so they can be served responsively.

Given the standard Elfinder package, you can bind methods to actions e.g.: https://github.com/Studio-42/elFinder/wiki/Logging#using-class-instance-callback

However, in this example the elFinderSimpleLogger class is initialised in the Connector file. Using laravel-elfinder, this file resides in the vendor directory so I don't want to change it.

The $opts array is available in the packages config file (config/elfinder.php) and in there I've tried to reference the new class:

'bind' => array(
            'upload' => array(new App\Classes\elFinderSimpleLogger(public_path('log.txt')), 'log')
        ),

But this doesn't work. So I then created a ServiceProvider to try and make the method available:

namespace App\Providers;

use Illuminate\Support\ServiceProvider;

class CustomElfinderServiceProvider extends ServiceProvider
{
    /**
     * Bootstrap services.
     *
     * @return void
     */
    public function boot()
    {
        //
    }

    /**
     * Register services.
     *
     * @return void
     */
    public function register()
    {
        $this->app->singleton('App\Classes\elFinderSimpleLogger', function () {
            return new \App\Classes\elFinderSimpleLogger(public_path('log.txt'));
        });
    }
}

but I have no luck here.

Should I be trying to override the whole controller or can I just extend the controller to provide a new method?

Thanks.