I don't know what to think of it, it seems to ridiculous to be true, but it would indeed be an incredible way to cheat.
Your title should've been:Motorized bike associated with Fabian Cancellara brought to you by You Tube.
Seriously at this point seems pretty far fetched, doesn't mean it would surprise me if this turned out to be true. Cyclists have already tried all kinds of invasive drugs, why not this? However Cancellara has displayed this kind of acceleration in the past. In his 2006 PR win he just rode Leif Hoste, I believe it was, off his wheel in a similar fashion.
Also at E3 Prijs this year he was alone up front with Flecha and Boonen and just timed his acceleration perfectly to win that race. Far lesser crowds at that race which would increase the risk of his two opponents hearing the mechanism kick in.
I would also suspect that the Saxo Bank mechanics would want to help the Schlecks take in at least one win at the Ardennes, which they didn't.
One last comment. I noticed someone say that Fabian is/seems like a nice guy. Well nice or bad guy has nothing to do with doping, chemical, mechanical or otherwise. Tyler Hamilton was and probably still is a nice guy. We all know that story, don't we?