How hard would it be to have a true xp mod?

After completing quests, each party member receives a certain amount of xp.

Take for example the starting dungeon in bg2. After you are out, there is a cutscene then the game will give a fixed amount of xp to each party member. But if you are alone, or have a party of fewer than 6 you are going to lose (amount of xp * every party slot free)

How hard would it be to make the pool be fixed but distributed amongst these that are inside the party, when you complete quests?