Not a direct solution to your problem, but people should definitely consider Apache over MIT when reaching for a permissive license. In addition to being more robust about things like, notifying users of modifications that have been made to the original source code, it also explicitly requires that forkers maintain the NOTICE file in its entirety, and distribute that file to users receiving copies of the software (whether source or binary copies).
Even if megacorp does nothing else for you, that NOTICE file can at least contain information about who you are as the original author, links to your website, etc.
I considered forking an MIT repo once but had no idea how to communicate which parts were under the original MIT license and which weren’t. Unless I copied it into each file and deleted the root license, it seems like it would license all my changes as MIT, too, basically becoming a copy-left license.
Even if megacorp does nothing else for you, that NOTICE file can at least contain information about who you are as the original author, links to your website, etc.