FCPX, converting stereo to 5.1 mix (without doing a total remix)?

I mixed the film in stereo. It might possibly be running in an IMAX theatre. An IMAX projectionist took my stereo and converted it into a faux 5.1, which he says works nicely. I've heard this can be done. I wasn't with the projectionist when he did it, so I have no idea what the difference would be on the big screen with those gazillion speakers.

I'm wondering: if I took the master stereo audio, put it on a new timeline, then switched the audio on that timeline to 'Create Space' ... and just output it like that ... would it give me a slightly altered mix, more amenable to a 5.1 system? Or would it have no effect whatsoever. I'm in the process of seeing if I hear a difference in my stereo system (very good Genelec speakers), but I'm not sure I'll hear any difference.

Any suggestions? Is there actually a technique where I can create a faux 5.1 without having to go into a studio with a gazillion speakers and taking a week or so to remix the whole film?

All ears ...