Create a new partition after Bootcamp
Winclone is the OS X software to backup and restore the Windows OS on a BootCamp partition.  http://twocanoes.com/winclone/

It lets you escape Apple's restriction to only have two OS partitions on a drive. You still might have to delete bootcamp, but you can then restore it in working form after you've re-done the boot drive partitioning to your liking.

Also see this question for core storage complications:


Can&#39;t reduce size of OSX partition in bootcamp