Just make several partlists, one for each sub assembly. For each part list, right click on the list to change list levels for selecting only one sub assembly (and its children), then right click on the list >> update part list and finally right click on the list >> settings, in the part list menu (left pane) you can change the starting number and the increment. Beware, you have to go to the part list settings, not the cell settings.
Sun