Can we? Probably not, there don't seem to be enough fissiles available: http://www.coarsegra.in/?p=95
The link in question analyzes the possibility of creating a doomsday weapon that could launch a projectile that would destroy all life on another earth sized planet remotely. That is a far more difficult task than just destroying life on the planet the bomb is on. The limiting factor in question is also fission materials to serve as triggers for the primary explosion in each of hundreds of thousands of shaped thermonuclear explosions. The massive numbers of distinct explosions are needed to progressively accelerate the Orion device but for a single explosion the ration of fissile trigger to fusion material need not be the same.
Mind you the Orion weapon is just intended to obliterate all life. That task becomes comparitively trivial when you aren't trying to do it across space via projectile. But if Multipartite literally wants to smash the earth into pieces I suspect he is out of luck for now!
He wants something which would crack the planet's crust; you're not going to get that with widely dispersed efficient-life-killing thermonuclear strikes (leaving aside the obvious question 'what do you do about the vents and spores etc'). To do that, you need a lot of energy, whether it's a kinetic projectile or a fireball & shockwave. A Project Orion kinetic strike would probably be more efficient than a pile of gigaton nukes since each explosion can be smaller and more energy extracted than it.
http://neo.jpl.nasa.gov/risk/2012da14.html
http://rt.com/news/paint-asteroid-earth-nasa-767/
Seems like a good opportunity to bring up existential risks. And A friendly reminder that NASA is in fact pretty damned important.
Thoughts?