Your question makes me wonder whether aliases would work, ie so you'd be able to keep a bunch of your user directory on the SSD and your Pictures, Movies, etc could be somewhere else, on an attached HHD. Your /Library etc could then be on the SSD.
It seems I'd done that, but my setup has been similar to Jay's since my wife took control of the MBB (MacBook black) and I'd moved to a mini. I wanted to be able to use both, but generally stayed on the Mini.
My user info went to a FW drive, and it was incidental to hook it up to whatever machine and use my current data. Both computers used the ctrl-click method to assign my user directory on another drive.
A caveat is that putting the machine to sleep whilst logged in would often corrupt the drive; Disk Utilities always repaired it, but I wasn't waiting for something permanent to happen. Generally logging out was sufficient to go to the other computer.
My current system uses that same FW drive; its a similar 27" 2011 iMac to the author's. I'd been looking for this option since having bought it; the SSD offered at the time was u$600 and it seemed just too, too expensive.