Murdock Mudeater wrote:
Or do I treat it as a routine, like preparing spells, and just inform the GM that "I perform my deific obedience..."
It's really going to depend on the deity. A lot of the good deities and their devotions can be hand-waved away pretty well. Others, like the Norgorber devotion you mentioned, aren't in that category. Thankfully, a lot of these will probably land you some alignment issues, naturally lending them to a "don't take" category. Unfortunately, this adds another layer of complication to that matter, which is... Unfortunate. So, in the end, you're just going to have to expect table variance, as per the norm on alignment issues.
EDIT: After looking through the core deities and their obediences, there's actually not that many that really cause a problem and can't just be made a part of normal preparations. Norgorber's is a pain to do to begin with and hard to not write off as evil, Lamashtu has you torture a living creature to death, and Asmodeus specifically dictates that your best subject is one who's unwilling (and better yet, one you own).