how can I configure a mac to modify parent directory timestamps when programs touch files
You should be able to use git-hooks with a post-commit trigger to read the push logs and then execute a shell script to touch your parent directory (or directories, if you wish to work up the tree). The push logs should contain all the modified files, so you can parse that information and touch the dirs accordingly.

This article may shed further light:

https://superuser.com/questions/740026/how-to-run-a-shell-script-on-git-commit

I hope it helps you to arrive at an efficient solution.