I'm not sure it would be cheating, since your main story would still be the diary. If you're allowed to quote whole poems, why not be allowed to have a character write a story which you've started?
My monitor is giving me a headache. I need a flatscreen like the other guys...
You're allowed to quote poems? Kewl. I put in one of my old lousy poems, but I felt guilty and figured on writing enough words that I didn't need to count those.
If I could really do that - include my other story, that is - it could solve a lot of problems. I might just do that.
Mmmm...flatscreen. My boss has a nice one. I have a hugh monitor, so I can't really complain...but flat screens are nice!