I'm helping out a charity with a website hosted on Wordpress.com. They use a 3rd party website to collect donations. They want to use a subdomain as a permalink to their page on the 3rd party site so they can change it in the future. As far as I can tell, Wordpress.com doesn't offer htaccess or equivalent.
So how do I make subdomain.website.com redirect to externalsite.com?foo=bar ?