You'll need to get a Sundriver yep.
It's a ODDE that replaces the DVD drive with a IDE or SATA HDD adapter.
The SATA one could probably handle an SSD and I'd say do it if money isn't an issue for future proofing but other then that, it'll never take advantage of the SSD speeds.
I've got a... 320GB HDD in mine and every game I threw at it loads just fine.
You could also opt to remove the DVD drive, gaffertape a SSD in there and have a USB lead leading out of the tray to the USB hub or you know, solder it internally.
You'll be limited to USB loaders tho.
tl;dr, yes it's possible but you must need some hard to find hardware if you don't want to hack it apart and solder some wires.