Laravel - Maintenance mode just for some urls

I need to use the "Maintenance mode" using the artisan command php artisan down, but just for some specific urls...

In my case, I want that all urls that starts with /admin continue working.

Is there a solution?

Suggest by @lukasgeiter I created a middleware that tests my url... That`s my code:

<?php namespace App\Http\Middleware;

use Closure;
use Illuminate\Http\RedirectResponse;

class Maintenance {
    public function handle($request, Closure $next){
        if($request->is('admin*') || $request->is('maintenance')){
            return $next($request);
        }else{
            return new RedirectResponse(url('/maintenance'));
        }
    }
}

After that I created a route that show de maintenance view:

Route::get('maintenance', function(){
    return view('errors.503');
});

Now I can call the command "up" and the application still under maintenance, but the /admin urls...