Long Neck[]
Creatures with Extra Arms, Extra Legs, or Strikers can take a Long Enhancement (+100%) which gives an effective +1 SM when determining that limb's reach; in the case of Extra Arms and Extra Legs, there's an additional rule letting you apply modifiers to the limbs that everyone gets automatically for a point cost of 1/10 the percentile modifier per affected limb.
Why not do the same for Extra Heads? Borrowing Long from the other Extra Limb advantages would allow you to to design extra heads with long necks, while borrowing the "modifying beings without extra limbs" rule would let you give a character with a single head a long neck. Doing this opens the door to adding other modifiers to Extra Heads while at the same time providing a means to apply their effects to a character with a single head. While I can't think of any others off the top of my head (no pun intended), that doesn't mean that there aren't any.
Obviously, it makes no sense to apply Extraneous to a single head; but that limitation would be the sole exception to the rule.