Well yeah, but let's say you radiate out as planned, but near the front of the spacecraft you expand a very large reflective dish, like a lightsail, say a km across. Now you're slightly biasing the direction the heat is radiating and the spacecraft will have to move in the opposite direction. Small changes in angle of the dish will move the vector of the reflected radiant heat.

In other words, you could use the main engines to get to Alpha Centauri, then use the radiant heat for the precision maneuvers around the system.