The way we do things will Buildbot is extremely hacky in many cases. We do clobbering, patching, and other things differently than we should. Buildbot has this functionality built-in in the form of it's Source classes -- we should have a ClientMkSource class that lets us take advantage of this fun stuff. Rhelmer has worked on one but it did not get finished. I'd like to do this sooner rather than later because it will help resolve bug 413906 -- which makes public Try Server Waterfall access a lot less useful.