I was thinking about adding something like that at one point, but I couldn't come up with anything I liked. The idea being that you might not want the hitbox to match the enemy's appearance, which ended up as SetOffsets() instead. Do you have a different purpose in mind?
Another possibility is that it could acknowledge the npc->DrawOffset variables and position the FFC where the enemy would normally be drawn. What do you think of that?
Edit: Actually, come to think of it, could you just use the npc->HitOffsets?