Stallman is perfectly happy avoid using your service and resources. His issue is that he doesn't have an easy way to tell whether or not he *should* avoid you.
It'd be fairly trivial for someone to put together a browser extension that refuses to execute any code that doesn't come with a copy of the GPL attached.
If the fact that nearly every HTTP response would end up at least 17k larger if the idea were to take off is too large to swallow; then just include a link to the GPL in one of a page's tags. It'd be just as easy for a user agent to check that as well.