Its not cheating to pre-plan Nano. Going in with a lengthy outline is actually suggested. As long as none of your preplanned stuff goes into the novel you're fine.
... Unless they've changed the rules heavily since 2008. o_O
As for me, if I participate it will yet again be 50k words of random crap that has plot holes the size of the grand canyon and weak if even there endings. So far I've done a Robot mary sue, a Reid/Donald mary sue, a Leo/Raph fanfic, and a sci-fi novel with a boy priest and a big burly prisoner guy and a civil war and none of it makes any sense whatsoever.
... Good luck!