[VX] Defend ability or Cover ability

[thanatos2k1]

Ok, I'm trying to think of a way to make an ability that allows a party member to take a hit for another party member,
ie.
"Cover" materia from FF7
or Cyans Defend ability from FF6.

Does anyone know how to do this?  Ideally I want to to be used in battle and only last the remainder of the round.