Question About Mixing With Ableton Live

Hey guys, now I know the start of this post may sound nooby but dont worry, I know ableton, I know how it all works its just a simple question and not a "HOW DO I SOUND LIKE DEM" question.

I am a huge fan of a lot of french producers such as Justice and SebastiAn. I love how they incorporate multiple genres into their sets, so I just have a quick question. I am interested in creating live sets very similar to Justices A Cross the Universe while using ableton with my MPD and Launchpad. One thing I just dont understand that justice does is mix music across such a broad BPM range. I know they do perform jsut regular DJ sets sometimes but their "live performances" that they do with Ableton are exactly what I'm lookin to do.

So basically my question is, how do I mix songs with different bpms in Ableton so they dont sound all weird and chopped up?

Thanks!

lots of different techniques, but the obvious one is to map the tempo to a knob or some buttons. http://www.heatercore.net/livetipslist.html thats the best place I know to get live set tips. super super good resource there, going from the real basics, to the real advanced.