I just posted to this lisppaste with a punt solution. Since this solution really has nothing to do directly with the problem stated, I thought I'd share it with you as well, with HTMLization and some editing from the original.
hdid -nomount ram://num_sectors (sector = 512 bytes = 0.5 K)
This outputs a device path (/dev/foo) on stdout.
newfs_hfs -v volume_name device_path
Formats the RAM disk as HFS+. See the manpage for other options.
diskutil mount device_path
The RAM disk will be mounted at /Volumes/volume_name.
You could also do something involving mount(8) instead of diskutil if you wanted to mount it inside
NSTemporaryDirectory(). Remember to unmount it (hdiutil detach device_path, or the Eject command in the Finder or Dock) when you're done.