That's certainly do-able and given that any spacecraft meant to leave the solar system would almost certainly use a Jupiter gravity assist it wouldn't be any more difficult to steer it into the planet itself.

However, if we were truly determined to get radioactive waste off of Earth and into space we could put it into an Earth escape trajectory and leave it in an orbit high enough so that it doesn't encounter the Earth again. That would save a ton of fuel.

We also have the option of impacting it into the Lunar surface. Radioactive waste is primarily a problem for us here on Earth because we have an atmosphere and a water cycle that causes particles to spread all around the ecosystem. But any waste left on the moon will stay put for billions of years because there's nothing to disturb it.