Direct link to a CSV-formatted report
This might be tricky because the export csv button actually runs functions to compile the file and force the download using php header() and content-disposition attachment. See line 224 etc here to look at how it is working: https://github.com/civicrm/civicrm-core/blob/master/CRM/Report/Utils/Report.php.

You could probably write an extension that invokes the functions to generate the csv based on what's going on here. Or perhaps one exists?