You could probably do something like this:
Initial situation:
[-NTFS partition-----------------------------------------]
Shrink that partition to half the disk size
[-NTFS partition----------][ Unpartitioned---------------]
Now create a HFS partition in the unpartitioned space:
[-NTFS partition----------][ HFS+------------------------]
Copy over all data from the NTFS volume to the HFS volume.
Delete the NTFS volume, resulting in this:
[-unpartitioned-----------][ HFS+------------------------]
And finally grow the HFS volume
However I would never try this without having a backup.
And if you already have a backup then it is much faster to just delete the NTFS volume and create a HFS volume. Which means the best solution is to borrow some extra storage space.
Shrinking a NTFS volume can be done with windows (7 and upward) build in utilities or with external tools such as gparted, Ntfsresize, Symantec partition magic or many other tools.
Growing a HFS+ volume is possible with OS X,using the included Disk Utility app, located in /Applications/Utilities.
Copying over the data either requires an OS which has drivers for both NTFS and for HFS, or a third location with is understood by both. (e.g. a pen drive formatted to FAT32). Apple has a Bootcamp HFS driver which might be the easiest solution.