The upgrade path should be changed so that there is a simple upgrade script that we run which will fetch the new code, diff and apply the changes.
You do realise that you just asked us to rewrite git, right? 😄
However, in any case, you're under no obligation to use git if you don't feel like it. You can download the tarballs here and copy them directly into the destination folder, overwriting files as necessary... although this is not really a supported upgrade step and I have no clue what could go wrong here.