Apple - How do I mount a sparsebundle to a folder rather than an image?

The hdiutil command-line utility gives you more flexibility, and is extensively documented in man hdiutil. Something like this should do:

hdiutil attach -mountpoint ~/myMountPoint mySparsebundle.dmg

You might also be interested in http://blog.marc-seeger.de/2011/02/06/encrypted-diskimages-in-osx/ which explains step by step how to set up auto-mount to the specified mount point:

• run mount to identify the disk device (/dev/diskNsN usually)
• run diskutil info /dev/diskNsn | grep UUID to get the UUID

• use sudo vifs to add a line to /etc/fstab

  UUID=whatever-you-noted-before /path/to/mountpoint hfs rw 1 0
  

• Add your disk image to your login items to have it automatically mounted on /path/to/mountpoint at the next login

hdiutil attach /Volumes/ATimeMachine/Pictures/iPhoto\ Library.sparsebundle -mountpoint ~/iPho

If this command is successful you should see something like:

/dev/disk3              Apple_partition_scheme          
/dev/disk3s1            Apple_partition_map             
/dev/disk3s2            Apple_Driver43                  
/dev/disk3s3            Apple_Driver43                  
/dev/disk3s4            Apple_Driver_ATA                
/dev/disk3s5            Apple_Driver_ATA                
/dev/disk3s6            Apple_FWDriver                  
/dev/disk3s7            Apple_Driver_IOKit              
/dev/disk3s8            Apple_Patches                   
/dev/disk3s9            Apple_HFS                       /Users/me/iPho

where iPhoto Library.sparsebundle is on a DroboFS (NAS) and is a 500G "hard disk" image formatted MacOS HFS journaled

Running the hdiutil command mounts the image under my home directory. I tired to mount it on top of the original iPhoto Library, but the original was still visible in there after mounting, so I changed the name of the mount point to iPho instead. Then I decided it didn't really matter where the mount point was, it would be fine under /Volumes as long as iPhoto.app knows where it is.

Option click iPhoto.app to launch it with a prompt to create a new library, and I did that in the mounted disk image. Then import all photos (previously managed with Picasa under a ~/Pictures directory tree) on my hard drive into iPhoto, which copies them into the mounted image, which resides on the NAS where it has some fault tolerance because of the DroboFS. This also frees up half the space on my small 500G SSD drive in the MacBook Air.