Is there a way to convert csv file to excel file upon request through apache/.htaccess
Yes, since apache is open-source, you can modify the .htaccess parser to call a library to convert your CSV files into excel files. But I don't think this is what you're looking for. :-).
I think really what you need is a dynamic web site. Then you can use PHP or any supported language to do what you need to do.
something like this: http://www.westwideweb.com/wp/2009/01/12/convert-csv-to-xls-excel-in-php/