Update:

the solution is there (here : ) : http://www.mobiphil.com/2010/03/git-on-shared-hosting-with-git-http-backend

Unfortunatelly the descriptions found on http://progit.org/2010/03/04/smart-http.html and http://ftp.sunet.se/pub/Linux/kernel.org/software/scm/git/docs/git-http-backend.html DO NOT work on a shared hosting. The apache configuration directives mentioned can be used only inside the global http.conf, but not on per directory .httaccess, where shared hosting users might have access. I will try to hack around to find a solution with rewrite, etc. that could be configured through .htaccess.