My personal suggestion for the proper reference to religion in the EU Constitution:
Neither the European Parliament, nor the Government of member state shall make any law respecting an establishment of religion, or prohibiting the free exercise thereof.
It is not very original, but it is a VERY good idea. I swiped it from the Constitution of the United States of America:
Amendment I
Congress shall make no law respecting an establishment of religion, or prohibiting the free exercise thereof; or abridging the freedom of speech, or of the press; or the right of the people peaceably to assemble, and to petition the government for a redress of grievances.
David F Mayer