[enkid]

You would have to decelerate and then accelerate to dock with each station. It would take more fuel then it would save by a lot. Edit: Alternatively you could accelerate the fuel, but it wouldn't be any better. You also have to worry about getting these stations in orbits that would be useful for the trip. Considering the Earth, Mars, and the stations would all have different orbital velocities around the sun, this wouldn't be an easy task.