Why does that have to be roleplaying?If you aren't using a skill such as persuasion or intimidate in a conversation, I'd say you were doing this thing called "role playing"*. Insight and other checks may influence what you are saying of course.
Insight as defined in the book is purely a mental/internal exercise no different than arcana, history or religion IMHO. It's getting a read on a person, that's all.
*Yes, I'm being a bit snarky here. But I can complain about answering the same basic question a dozen times as well.
Approach 1: give dialog demonstrating the intent (roleplay)
Approach 2: state the PC is asking probing questions to gain insight (mechanical action)
Approach 3: state the PC is using insightfulness (DM knows this can be probing questions as a possible method and adds that to the dialogue to help develop the player's future statements).
Just like there isn't anything wrong with simplifying a task by speaking in game mechanics, there definitely isn't anything wrong with roleplaying in a roleplaying game. My position is don't force the roleplay to the point it affects using game mechanics.
Insight as stated by the rules:
" Your Wisdom (Insight) check decides whether you can determine the true intentions of a creature, such as when searching out a lie or predicting someone’s next move. Doing so involves gleaning clues from body language, speech habits, and changes in mannerisms."
Involving gleaning those clues doesn't preclude an active approach to triggering, and an omission of statement does not prove it's invalidity. What that means is it doesn't say it's on only a mental exercise; nor does it say using a real-world approach like probing is invalid. It doesn't actually give specifics on how at all -- only some of the things involved.
I would say it's hard to glean clues from speech habits without engaging in the speech part. ;-)