Have you looked into A New New Testament? They have some great background stuff there (including source documents). In that book, it suggests using The Letter of Peter to Philip to read alongside Hebrews. There are some very unorthodox things Jesus says about God in that Epistle. Sorry, I know it's not Pauline but thought you might be interested anyway.
EDIT: Also, maybe The Acts of Paul and Thecla which is included in the same source. That does not necessarily claim Pauline authorship, but does include the Apostle. It's really more about Thecla, but does include unorthodox views.
Non-mobile: A New New Testament
That's why I'm here, I don't judge you. PM /u/xl0 if I'm causing any trouble. WUT?