The fastest way, given your current setup, would be to use the autotracer feature, under the layer menu. You either have to give it a precomp with an alpha trace or at least a contrast trace, then tweak the settings using the preview feature and autotrace for all the comp duration, then wait. Keep in mind that if you change any parameter of your original trace after the autotracing is done, you have to autotrace it again (it is a static feature, that does not change dinamically with changes you make afterwards).
Hope it was helpful.
Leo