How to store sleepimage on secondary HDD on Mac OS X 10.6?
Nice HDD setup!

Load Terminal.App in the utilities folder, and use the following command:


  sudo pmset -a hibernatefile /Volumes/OtherVolume/sleepimage


Obviously change /OtherVolume/sleepimage to /YourOtherVolumesName/sleepimage 

From explanatorygap.net.

(EDIT: that webpage shows even the author did not succeed with this method. Likely reason is the other drive is not ready to read the image when trying to wake up. Apple says the sleepimage must be on the root drive. I myself am getting a crash when trying this.)