There is no solution regarding this. Regarding links from messages to profiles, you may try to achieve it modifying parseMessage() function, but other than that, if a linked username appears somewhere else, it would require core modifications.
Personally, I don't see much sense to implement such links. Such links obviously don't add anything SEO-practical or usable, 'cause all profiles in miniBB by default should not be indexed. And the profile, basically, is not the most important thing in forum software ;)