Knowing it's trajectory and throwing something at it fast enough are two very different things. There's no planets between here and there that we could sling-shot off of. Even if there were, we don't have anything to send out to it.
The trouble is computing these trajectories is pretty tricky and if you get even one manouver wrong you crater or burn up in the atmosphere.
If our craft can accelerate fast enough to intercet it, it’s position is still irrelevant since we know it’s trajectory.