Use WordPress in a subdirectory.
Make sure your WordPress code is in the root directory of your site and is called wordpress/.
You can set the sub directory in the constructor function of the class code, rather than the sub directory needing to be wordpress/.
All you need to do is change the value of $this->subfolder = 'public'; to something else. Note the missing trailing slash.
Just move WordpressSubDirectoryValetDriver.php into ~/.valet/Drivers.