Easy Expat actually has a guide on Sao Paulo that may help you find what you are looking for (http://www.easyexpat.com/en/sao-paulo.htm). In the section on language courses (http://www.easyexpat.com/en/sao-paulo/s ... ourses.htm). They list:
Portuguese Language School in Sao Paulo has been devoted to providing high quality and personalized instruction in Portuguese for foreigners. All of their teachers are both native speakers and university graduates who have been trained in a direct approach to Portuguese language teaching.

and www.languagecourse.net/schools-sao-paulo.php3

In answer to your question about USP- it looks like they take non-students for language courses. Here is their info: http://www.usp.br/internacional/home.ph ... &idioma=en

Best of luck!