Low-Bypass Solid Rocket Booster

An idea came to my mind when I thought about replacing the Turbofan engines with the solid rocket boosters for my Stage Zero design. Turbofan engines are fuel efficient because they utilize the bypass air in their total thrust. Why don't we add a casing around the solid rocket booster like the one around a turbofan engine. The casing will collect and force the air to pass around the rocket's nozzle. Unlike a turbofan engine there wouldn't be a fan to compress the air. Therefore, it's effect would be minimal at lower speeds, but as the plane speeds up it would add up to the total thrust. This design would only work on Stage Zero solid rocket boosters. It wouldn't work on a Space Rocket launched at high altitude due to lack of air.