How can I resize my Lion partition to fill up the unused space on the drive?

Question

My MacBook (Late 2007) has an 80GB hard drive. I used to have a 15GB Boot Camp partition, and deleted it at some point -- but I forgot to resize my Snow Leopard partition to fill the 15GB of free space at the end of the drive.

Since then I installed Lion. When I start from the recovery partition and try to resize it, Disk Utility fails with the error: Couldn't unmount disk.

I'm guessing this is happening because the 500mb recovery partition (which I booted from) is in the way. Here's what I get when I run diskutil list:

/dev/disk0
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        *80.0 GB    disk0
   1:                        EFI                         209.7 MB   disk0s1
   2:                  Apple_HFS Macintosh HD            65.3 GB    disk0s2
   3:                 Apple_Boot Recovery HD             650.0 MB   disk0s3

How can I move the Recovery HD partition to the end of the drive so I can resize my main system partition and get that 15GB of space back?