So I guess in that case part of the trick is confusing himself.

If he’s not sure what he said, it’s tough to rule it as a lie.

I guess it depends on if the nose grows with untrue information, or lies.

Because if it’s lies all he needs to do is THINK it’s the truth and his nose won’t grow.

If his nose grows because the information is not true, then this is one hell of a power. You could get him to theorise on the meaning of life.