Ok just tore mine down thinking I could easily add a SSD drive to my 1TB sata setup. NOT. There is NO additional SATA port and the one that's on the MOBO is proprietary to Apple. So unless you have a converter that can adapt a STANDARD sata cable and power, then adding your own "Fusion Drive" setup is not going to happen. However, if you bought the SSD model then you can add the additional HDD but would still need to split power from their proprietary power cable. UGH.
Save $15 dollars and use a plunger. Works perfectly.