One would hope that this technique is not something simple like... linking to the
non-canonical link, adding irrelevant get and anchor tags to URL's pointed at the domain (like Urchin/GA variables), providing the domain's IP address (every webserver has an IP, after all), et cetera.
Each of these methods will create a genuinely "different" URL, though I honestly doubt that penalties are attributed in most cases.
The "penalty" for having multiple URL's point at the same content is the dilution of the content's ranking under a single URL. Search engines like MSN and Yahoo will still list each link (if memory serves), though the content will have multiple links of lesser weight than a single link would... but if you're spamming competitors' links in an attempt to get them penalized, you are essentially contributing to the greater likelihood that the links which you are providing are
helping their content's ranking under different URL's...