That's very clever. There is one problem though, now make clean all install is run as root (well maybe install stages now in homebrew). Imagine an env var not set (the way make vars interact give lots of way to shoot off a big toe here) and the wrong dir gets rm_-rf_-ed or it obliterates something in /bin instead.

If you don't run brew as root you at least protect places like /usr/lib, but you are protected from that and more with macports (where stages and uses nobody).

But for now your approach seems the best pragmatic course to take, thank you for the suggestion.