If you DID decide to dump in 2 L of starter, you still wouldn't need to take it into account for the total volume, since technically you'd be dumping in already-fermented wort (fermented from the yeast put in there to build up their volume and numbers).
Personally, if it's over 1 L, I always put the starter in the fridge for a couple of days before brewday (after it has fermented out)... this way, the yeast will floc out and settle, and on brewday you can take it back out of the fridge to bring up to pitching temps, and decant off most of the liquid, so you're pitching mostly yeast, instead of yeast + 2 L of fermented wort.