[firedrake] using different petsc version

Dear Firedrake-Team, this may be a question that is very easy to answer, but I didn't get it working by myself. I would like to use a different petsc version which contains some small changes. I am using firedrake inside a Docker container, where i run the firedrake-install script. I tried using PETSC_DIR with --honour-petsc-dir, but this fails with some missing include files. Is PETSC_DIR only the source directory of my own petsc version, or do I have to compile it before? Is it somehow possible to just specify an individual url / git-repository to use a different petsc version? thanks for any advice Florian