I'm replacing the stock drive with an SSD and was wondering if its possible to put the stock drive into an enclosure and connect it via USB to the MB for backups etc
Yes, it is possible. I bought a Acomdata Tango FW400/USB combo case for $30 or so. With this case, the computer really doesn't like to boot with the Firewire which is a disappointment, but for day to day use it works well.