honestly you don't even have to roll secretly. Simply withhold the DC, and give them something.
for instance if the dc is 18 really high for many reasons. they roll a 12.
'You really can't get a grasp on this person.' or 'The person in question believes what they are saying.'
Example one the person is hard to read, so you don' t know. Example 2 You find out the person believes what they are saying to be true. Weither or not they are lying isn't stated, and left to the player to decide.
That's fine, too. As a player, I generally find "You rolled really poorly. It's not that you can't get a handle on this person you're talking to - you confidently and wildly misread the cues." situations to be a lot of fun and often lead to more interesting RP.
Sure, inaccurate information on low Insight check rolls is one thing you can do in tabletop. I'm proposing "does the DC of skill checks get revealed, (yes/no)" because that seems fairly simple, and the less complicated the new feature, the more willing Larian would be to entertain the notion of adding it.