Deactivate self-upgrade functionality

I recently helped package ghcup for Homebrew. See Homebrew/homebrew-core#93865. However, Homebrew policies require disabling self-upgrading features in packaged software, something the current Homebrew formula doesn't meet yet.

Thankfully, ghcup is conscientious enough not to tamper with installs outside where it expects to be, so the self-upgrade functionality doesn't break anything. However, it probably doesn't function the way users would expect it to.

Is it possible to provide a way to pass a flag to cabal to disable the self-upgrade functionality? Or, alternatively, if there were a minimal patch we could carry in the formula to do so, I could probably apply that as well. I'd appreciate tips here, however, since I'm very new to Haskell.