My custom python file to generate python scripts for every click

I unlocked the default python buildpack and added a few lines that basically add phantonjs and casperjs executables to my environment. The code is here: https://github.com/tapanpandita/heroku-buildpack-python . The changes I've made are minimal (from line 163-196 here https://github.com/tapanpandita/heroku-buildpack-python/blob/master/bin/compile#L163 ).

However, now the problem is that when I click on masterkus heroku all requirements are loaded again. This makes the deployment process very slow. This was not a problem before when I used the standard buildpack. Any idea what I could have done wrong? This is a django app.