Yes, Disk Utility can’t edit space in the “middle” of the disk, only space on the “ends”.
There is an app called iPartition that sounds like it does what you need. From the website:
iPartition makes it easy to create, destroy, resize or format partitions on your hard disks, whether internal, external, fixed or removable.
Two caveats: first, I’ve never used iPartition myself, so I can’t comment on its reliability. I’ve used their other product (iDefrag), which was very stable and I’d recommend, but not iPartition. Also, according to a blog post (http://www.coriolis-systems.com/blog/2011/07/lion-compatibility.php), iPartition doesn’t work with Lion FileVault partitions. Don’t know if that affects you.