i don't mean to burst your bubble, but it's not gonna work. if it did work like that, pc motherboard makers wouldn't need to add costs to their motherboard by adding additional sata controllers that are external to motherbord chipset (north/south bridge). It's not like a usb port where you can have 127 devices to one port.
and even if you don't blow up your ps3 or both your hard drives; how do you think the ps3 will decide which hard drive to talk to? It talks to the device attached to the port... it's not gonna talk to both drives. at best, each drive will be given the same commands - will read and write the same data. I say 95% chance you blow up your ps3 or kill the sata port.
some stuff for you to read: http://www.ata-atapi.com/sata.htm
SATA supports a single device per SATA cable
the above page speaks negatively about SATA, cause it is a PATA based site.
SATA stuff can be found here: https://www.sata-io.org/secure/spec_download.asp
but you need to buy the specifications if you want to read them.
Good luck on your experiment