Originally Posted by Daniel_

Sadly, it's already been thought of, and discounted.

Although on a micro scale steel appears incompressible, on a mega scale it is quite spongy. Pushing on one end creates a pressure wave that travels along the rod at around the speed of sound in the material, and causes the other end to move. Steel has relatively high elasticity, which is why we use it for springs. The scheme would work better with something very hard, like diamond, but you'd need a diamond five light years long, and thick enough to support the lateral stresses that this would generate, otherwise it would shatter.

Even if you could allow for an area of spacetime that was flat enough to build such a rod without it being so flexed by gravity that tidal effects would give a signal to noise ration worse than 1, the inertia of the steel would mean that you're trying to push gajillions of tons of steel backwards and forwards - this would take more energy than the total output of the sun (assuming that you could overcome the fact that you'd need the mass of several earths to harvest the steel.

Therefore, to make this scheme work you'd need the following:

Interstellar travel
The ability to negate inertia
The ability to generate instant huge levels of thrust in excess of the output of the sun
The ability to harvest all of the iron and carbon on multiple earth sized planets
An area of spacetime that is totally flat.
A material so dense that the speed of sound in it exceeds the speed of light.

Basically, by the time you've got inertial dampening and huge amounts of free energy, you can accelerate to light speed instantly, and travel anywhere in the universe in aproximately zero subjective time - so why bother with the long stick?