Originally Posted by cavernmech
If that old tandem is from Cogs it is fixed...perhaps not the best choice.
Yep, that's the one. So I was not so off-topic after all!

You're right, however: I'd ride fixies and tandems separately, but they are a combination to be considered with caution.
Warren Cycle Works on Queen East has an old CCM cruiser bike tandem in the window...it is certainly not new so he might be willing to rent it out. Be forewarned though...the guy in there is a bit surly and can be hard to deal with.
Cool; I know that place! I worked in a cycling camp that ran nearby last summer and we took kids for a sort of a field trip there on a rainy day once. Seemed like friendly folks, actually.
You may want to try Sandy's Cycle up on Laird...they are tandem specialists and might have something for you to rent. Maybe try a Craigslist ad...someone out there prolly has one they would be willing to rent.
Thanks for all the suggestions. I really didn't expect so many leads so fast. This thread rocks.