Yeah, its gonna be tough finding something that actually does a good job of emulating a 12 string Ric... as was mentioned, you could record a guitar part, and then capo at 12 (if you're playing a strat I believe this is possible), and re-play the part. As for the Rickenbacker tone, I wouldn't know where to start in terms of emulators, I've never heard an even halfway decent one.
The problem with octave pedals is that they bump everything you play up an octave (if that's the setting you have turned on). On a Rickenbacker 12 (or any 12-string, I guess), I believe its the high three sets of strings that consist of one normal-tuned, and one tuned an octave up, and the bottom three sets are all tuned to the standard octave. So, you don't end up getting a muddy sound from the lower strings... with an octave pedal, you would be doubling the bottom-end up an octave as well, and that can make your sound thicker in the midrange, and a bit muddier. However, I've heard some decent octave pedals... ElectroHarmonix makes some good stuff, but it is a little pricey. I'd say hit a local guitar place and try out what they have.