It's been a long time, but I remember not liking the C-stick so I stopped using it in Luigi's Mansion. I have no idea if that was an in-game option or if I just chose not to touch it. Though now that I think about it, you might have to hold both sticks in the opposite direction of the ghosts to wrangle them, so maybe I just used it when it was necessary.
Regardless, Luigi's Mansion 2 was in development before the second slide pad attachment was created, so they've already created a normal control scheme. I do think the game will be compatible with the attachment because it would make some sense, but not a requirement.