Doesn't work when SConstruct file is not in the current directory

I've got the current directory in vim following the current file, by using:

    autocmd BufEnter * silent! lcd %:p:h

If I'm editing ~/Source/foo/bar/baz/quux.cpp, and there's a ~/Source/foo/SConstruct file, makeshift walks up the directory tree and correctly decides that I want to use scons.

However, it then runs it from the current directory, and scons complains with: `scons: *** No SConstruct file found.`

Is there a way to get it to invoke scons from the correct directory?