Wow, I think you really should talk to the landlord and explain your situation. It's just not fair to force a cat to live where it might be "evicted." What happens when the landlord catches you coming from or going to the vet with a carrier? What if they do an inspection and find the cat? What if they do see the cat in the window? It gets sent to the pound and put to sleep? Or if you do keep the cat away from the window, don't you think that would be quite boring for the cat? Windows are "cat TV," as Ingrid Newkirk put it. Especially with a single cat, you'd have to work hard to provide it with sufficient stimulation.
Also, you give cats a bad name by being deceitful. You should explain that you're a responsible cat guardian. Assure the landlord that you're well aware of neglectful cat owners who don't take care of their cats and let their cats damage property, and that you actually encourage landlords to step in and stop the property damage and animal abuse in such cases, but that you're not one of them.
If the landlord catches you, he might just think "Oh well, they proved yet again that anyone with a cat is a lying, untrustworthy person, I'd really better never allow cats" and that just makes it harder for anyone with a cat to move in later.
Please take a look at this for more information: http://www.pets911.com/information/p...ting/index.php
That said, I do find that anything sticky cats tend to avoid. When I was growing cat grass in one windowsill and didn't want the kitties getting into it just as it sprouted, I put tape sticky-side up about one and a half cat body lengths from the pot on the sill. It worked fine.