Recently I noticed that somehow my 40 gallon tank had gotten a small chip in one of the corners. Though the chip was small, I didn't like having the sharp edges exposed. I set about trying to remember what sort of abrasives I had around the house with which I could smooth the glass out.
The first thing that came to my mind, and in fact the only sufficiently fine, hard abrasive I have, is the crock stick knife sharpener http://www.amazon.com/Lansky-4-rod-C.../dp/B000B8FW0E
I keep in the kitchen drawer.
The ceramic rods that come with this sharpener, especially the "finishing" rods are hard and fine enough to smooth chipped glass corners. Use light pressure and keep the surfaces wet as you're working. It only takes a few minutes to remove the sharp edges. Also, chipped corners are somewhat less noticeable because they aren't as jagged.
This method has limitations, clearly, but it might be just what you're looking for, especially if you already own a crock stick.