According to the SFLC document, consent only needs to be obtained if the permissive license is to be retained.  Re-licensing of work already covered by a permissive license can be done without consent (and is indeed done all the time; Microsoft didn't ask anybody when they appropriated the BSD TCP stack and relicensed it as part of Windows.)  I'm skeptical that it even needs to be done in the cases the SFLC describes, as that sounds more like a GPL-induced requirement than one pertaining to permissive licenses, which are far less restrictive.