I'm actually interested in this as well, and have done some research in the past. Here's what I remember from when I looked shortly after release.
If you installed from the CD, no, you cannot use a NO-CD. I believe they exist, but if steam connects, you're screwed. It does an exe check each time apparently.
If you installed from a steam Download, there is a way to play offline and this is effectively the No-CD way. I have read of a way to convert your CD install to a steam install (something about copying certain folders around) but I don't remember the specifics. It's definitely been posted on other gaming websites so a search should turn it up. Search for "offline mode" when doing so.
Other than that, there is no straight NO-CD.