Internal SD to External SD Init.D Script
You must have the latest version of Freedom Kernel Overclocked or Lite.
Here it is. I've never used it, but seems pretty straight forward...
Make sure you read read read!!! Did I mention to read lol?
[SCRIPTS]CronMod-INT2EXT (updated 02/28) - xda-developers
You will need an EXT4 partition on your external SD. You need a ratio of 5 to 1, for example: If you have 1gb of internal SD space then you will need 5gb of external SD space in your EXT4 partition.
Here's a tutorial to help you partition your external SD... Link Here