The triggers you need are Position state and Rotation state. Assuming you have the hand in position on the hip, you need to define in that pose what the hand will be parented to, say female hip. The trick is, you leave the Position State and Rotation state to On, which means it ignores the parenting. When you want it parented, set the triggers to Parent Link, then set them back to On to disable the link. Here's an example with a Physics Link, but the concept is the same. Don't leave the state in Parent when changing poses, or the models may get twisted up.