No...I don't have a secret method of BitLocking a single partition. But my buddy John Baker posted about a tool that will reconfigure your machine for BitLocker if you decide to implement it after you have already configured your hard drive as a single partition. I am performing a Complete PC of my laptop right now and will attempt the tool once I am complete. I will post my results when done...
*** Updated 1/21 *** The BitLocker Drive prep tool worked exactly as promised. It only took about 5 mins total to prep my drive. Then of course it is still a matter of walking through the BitLocker wizard to actually encrypt it. I have about 50 gigs in my OS partition. It took about 20 minutes to encrypt the whole thing.
This tool works like a charm, even better... ;-)
read this post: http://blogs.infosupport.com/ericd/archive/2008/01/15/Bitlocker_2C00_-laptop-and-server-2008.aspx