The only way i see you can do this is by standing near The Plaza when watching the parade, then right afterward, go to the dessert party. Your table is already pre-assigned before you get there, so you can either be the first or last in line, and you'll get the same table. You have no choice in the matter there. It's pot luck if you get "good seats". Regardless of where your seats are, you are instructed by the CM that you may stand at the railing to view the fireworks.
If you take a look at the pictures at the beginning of this thread, you'll see that there are very few tables you can actually sit down at and view the fireworks.
Also, If you see all of the parade first then attend, keep in mind that the dessert party will have been going on for a while already. There will be desserts there when you arrive, but as to how much, i have no idea. Someone else here may have more information on that.
Hope this helps.