I don't think there are any Thunderbolt SSD enclosures, and probably wont be for a while... The only thing I can think to do is if you already have an SSD buy something like the above and then swap out the drive yourself... voids the warranty but a cheaper way around it.
Could always replace the optical drive with an SSD for a boot drive and then have an external optical drive. Safer option imo just so you avoid the slim, but plausible chance that it gets knocked/disconnected while you are in the middle of something.
That Elgato unit also has just 1 TB slot, meaning it has to be at the end of the chain...very annoying if you have a display, then video I/O then the drive.. you'd have to shut down before you could do anything like disconnect your display..not convenient at all really imho.