Unless you have a way to spin off the yeast, chill it and rack above all the settled yeast, or stun/stop the yeast and add potassium sorbate, adding apple juice will get fermentation going again.
I'm not sure exactly what you meant in your question about "adding apple juice to the pour off before bottling and get carbon dioxide in sealed containers" ... but if you're asking if you can add juice to the fermented cider that you are putting into bottles, and have those sugars in the added juice get the CO2 into the bottles- yes. Exactly how much juice you should use, however, can be tricky to calculate. You can take a gravity reading of the sweet juice, and calculate how much potential sugar is in it, and do the math from there to find out exactly how much you'll need to produce enough volumes for your cider.
It only *needs* to be pasteurized or chilled immediately after bottling if you plan on killing or sleeping the yeast so it doesn't ferment the extra sugars from the added juice (sweet/still cider). If you want dry and bubbly, then you need to leave the capped bottles at room temperature for a week or more for the yeast to eat and make the CO2.