My friend and I did it (cycled ON the canal) too. Same day or thereabouts I'm sure. Very glad I did too. My wife was horrified at first... but we'd thought very very carefully about it and even assessed what tools for rescue we were carrying.
To be clear for anyone who wasn't in Edinburgh in 2010 - it had been VERY cold for substantial period. Don't try this on a normal Edinburgh winter! I don't suppose anyone can remember another year this was sensible. Would be interested to know if there was one.
Like the letter. Two people pushing bikes cause much more risk of an upset then one riding (and paused) and one pushing. The only think I worry about is whether anyone checked the integrity of the railing when I lean on it...