Using a stdClass instead of a mock

Question

I have had a few situations where...

• I cannot use a normal mock because the object being mocked is hard coded (ie uses new SomeName() instead of using dependency injection ways). [and...]
• I cannot use Mockery's alias: or overload: mocks because the class has already been loaded. [and...]
• I cannot use Laravel's facade mocks because the class is not a facade.

So as a last resort, I have created a class within the same file as the test, called Mock_Class_Name and used PHP's alias() function to replace the real class that I want to mock with my class.

A problem with this is - unless it is a Laravel alias - I can't simulate any sort of partial mocking so my class has to define ALL functions which get called and not just the ones I want to mock. (If it's a Laravel alias which is being mocked, then I can just extend the real class but that does not work normally.)

Pseudo example:

class someTest extends TestCase {

     publicfunction firstTest(){
          class_alias(Support_Class_Mock::class, 'SupportClass');

          //// rest of test code here

     }
}

class Support_Class_Mock extends \App\SupportClass

{
    public static function oauthGetAccessToken($beep,$boop){
        return 'OAuth Successful';
    }
}

My question: Is what I am doing an acceptable "last resort" practice? (Or is there a better way?)