a framebuilder could replace the seat tube - cost would be close to that of a new frame.
remember you'd have to re-paint, too.
if the dents are small enough, you might be able to push them out from the inside, just by jamming a long seatpost or similar in there. not exactly high-tech, and: if there's any kind of crease or a shape that would lead to stress cracks, it's only a matter of time till cracks form. however, it's likely to be a pretty long time.
most likely from the scenario you describe, if they're just cosmetic, put some touch-up paint on and move on having learned your lesson.
(yet another in the very long list of reasons that steel is a better real-world frame material)