well if you can get pumice like from volcanic rock you need it in power form and you can polish the glass but you will remove the protective coat if there is one just mix the pumice with distiled water and polish in by hand
this is what we do for the Dodge Vipers that come through here we polish the windows and they arent scrached but this makes they eiser to see through and you can see the difference when done
we have a half done window we use for showing customers what it will be like
I think with some patience this will work