I would be surprised if just adding a turbo helped FE in any way.
Using a turbo to bring a car back to "acceptable" performance when something else has been done (e.g., lean-burn, downsizing the motor, etc.) is a well-trodden path to FE. Just ask anyone with a Cruise Eco.
It might be fun to run a 1st-gen Insight 3-cylinder with a turbo in a CRX.
-soD