Well, it actually may have been really simple, but sadly SNS in its entirety does not exist anymore. The games have been hacked to pieces, and the truth is that Rare unfortunately was forced to drop the feature from BT when Nintendo changed the way the N64 works. There was a lot left over in BK, not expected to be found, so they put the game paks in BT to appease those who finished the game with 100 Jiggies and saw Mumbo's Pictures. The Ice Key get you the transformation in Ise O' Hags that makes Kazooie a fire-breathing dragon, is all.
Oh well.