Enable cross-origin resource sharing, CORS, woocommerce multisite, HTTPS, domainmapping

Please read I have a multisite instalation, and one of the sites are running the "Fancy product designer" plugin. I get an CORS error when I try to load the designertool Link: [login to view URL] So it seems that domain mapping does not work on media files. I see 2 solutions: 1 Allow CORS in the code Header set Access-Control-Allow-Methods: "*" in htaccess does not work. 2 Get a working domainmapping for media files What is the best solution? I am not comfortable shearing FTP access or wp-admin access.I want someone who have experience with this to tell me what to add where.