I just renamed my Windows partition so it can sit there next to my OS X partition. You have to do this in Windows, of course, but using Windows is why you have the partition in the first place, right?
Also, since I have Parallels use my Boot Camp partition for the VM, it "unmounts" the partition by itself when it starts. The annoying part is that sometimes the partition comes back after Parallels exits and sometimes it doesn't until I restart.