No no no. Surely it would be easier to build a forge, modify it so that it's stupidly hot, take silica sand, and melt it into liquid glass. Then, you spread it over top of the scratch. Then buff it smooth. Do this while water is still in the tank so that the water can act as a coolant, making sure that the glass doesn't shatter under the heat stress.
Has anyone actually tried those car windsheild buff kits? Personally I agree - I don't see how you can do it without the buffing itself creating a bigger problem than what you had before - but like I said you see these things being sold all the time - I almost wonder if it's worth just trying it on a piece of scrap glass just to see how badly it would turn out?
I suppose if a scratch is on a non-viewing panel you can just paint over it. But on a viewing panel I think the options are to live with it (if the tank is running), or replace the panel (if the tank is empty).