To me it should be spontaneous. I know that I am always deeply touched when a sub speaks of herself in that way, but I never try to force the issue. If it is not natural, why would I want it?

Just my opinion there, but I do know of a few Doms who prefer that their subs speak that way. I would talk to him about it, and try to get him to understand that it does not come naturally. Submission is a gift, and him trying to puish you too fast will only push you away.