Well, depending on whether a script tag gets its own context, and each context gets the same seed (in which case you're boned?), you could use an extension of some sort that runs a random number (through your own pseudo random function with time and/or page location as seed inputs) of Math.random() calls to mix up the results.

Or just use an extension that replaces Math.random() with something more random, but it's possible that could cause weird performance problems on certain pages and it would be hard to debug.