Don't install 3 prong outlets without a grounding conductor. That's taking a bad situation and making it worse. No inspector should approve that. The only way you can install 3 prong outlets with out fixing it (making sure a grounding conductor is present and connected in all recept boxes) is to install a gfci in the circuit. Either by adding a GFCI outlet at the first box in the circuit or replacing the breaker with a GFCI breaker.