"Well I said might." Harry told him, "So no guarantees but we can see if I show you a few things your father hasn't seen." Lowering his voice slightly, though he knew Severus would still hear him, "More likely is I'll show you things that I'll get yelled at later for." Like the passage to Honeydukes maybe. He was sure he could sneak upstairs to get a few treats without Colin knowing who he was with. He could just say he was making sure the tunnels hadn't been disturbed.
He then shot a wink at Faustus, "Or we can always prank the students and you can laugh as McGonagall scolds me and reminds me I've been grown for many years." Though if they used the invisibilty cloak maybe they could get away it.