I was recently helping to replace CV boot on Xterra and as part of the process we had to separate CV joint. FSM draws nice sliding hammer and says if it doesn't - replace the axle. As we didn't have a sliding hammer nor were willing to buy the axle we came up with technique on our own. Unfortunately you can see only outer part of CV after separation as I forgot to take the picture before the action so use your imagination . The idea is to bolt something to the outer part which would be of bigger diameter than the CV itself then you put the whole assemmbly between 2 strong supports with height about 1.5-2 times of the axle length. Then you lift it few inches up and quickly drop down between supports holding both parts with your hands. When the bolted thing will reach the supports it will sharply stop the outer CV part while the bottom one will continue its way down due to inertia. It took us 2 hits to separate the joint. I think, it will always work as bottom part is quite heavy. Please use this at your own risk, usual disclaimer applies.
We used a puller and 2 rails from the engine hoist which you can see on the pictures:

 

I don't think the pics are big enough....

 

Oops, didn't realize how big they actually are.