Contrary to your assertion that this phrase cannot be used, I assert that the word "discipline" is not just "a discipline = a praxis", but also "discipline = a set of rules of behaviour".

So semantically, the "arcane discipline" could be exactly what you describe.

Googling this gave a few differing examples:


http://www.lcms.org/ca/www/cyclopedia/02/display.asp?t1=D&t2...

Disciplina arcani

(Lat. “discipline of the secret”). Term used since the 17th c. for the withholding of certain parts of Christian teaching and worship from pagans and from catechumens till the last stages of their preparation. Some scholars find an approach to this practice in some NT books (e.g., Rv). Justin* Martyr seems not to know the practice but there may be traces of it in the ch. order ascribed to Hippolytus* of Rome. The most extensive use occurs in the era of mass conversions after the end of the persecutions AD 313 (see Persecution of Christians, 4). At this time it included the rites, ceremonies, and statements of the significance of Baptism and Holy Communion, and such liturgical forms as the Creed and the Lord's Prayer. The arcane discipline disappeared almost wholly in the 5th c. ACP

http://www.phoenixmasonry.org/arcane_schools/part_3.htm
ARCANE DISCIPLINE. This system was in vogue in the church of Christ between the first and fourth centuries of our era. ....



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Note added at 20 hrs (2007-01-18 18:09:56 GMT)
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Here's a very extensive entry, which directly links the above Latin term to your German term, under the English entry

"Discipline of the secret"

http://www.newadvent.org/cathen/05032a.htm