This is defacto your only option:

http://www.tim.com.br/sp/para-voce/p...go/tim-visitor

Go to a company owned TIM store with your passport, some basic portuguese and patience for bureaucracy.

You cannot get a 'local' sim without a tax ID number (CPF). Other operators launched tourist sims around the time of the world cup, but there are many reports on the internet of difficulty getting them since.