the meaning of "piggyback"

[kjc0123]

What is the meaning of "piggyback" in the following sentences?

The mysterious summons, Aringarosa suspected, was probably a photo opportunity for the Pope
and other Vatican officials to piggyback on Opus Dei's recent public success�the completion of their World Headquarters in New York City.

[Quizmonster]

Usually, a 'piggyback' is what happens when an adult carries a small child on his back, with the child holding around his neck and with its legs wrapped around his waist. It is used in other situations such as where one organisation takes advantage of another in order to improve its own performance or to raise its profile. For example, a politician who wants greater police powers might use a recent dramatic rise in crime to improve his case. He is, in other words, 'riding piggyback' on the crime-wave. 

[Clanad]

The origin of this phrase is interesting...  One source indicates the original phrase had to do with stacking objects in storage. Each successive object was laid on the back of the other in a manner described as "pick-pack", and from there the idea of something being carried on one's back it came to be called "pick-a-pack", and from there it was an easy, (albeit insane) leap to "piggyback". Yet another source states authoritatively,  "Instead, piggy back is an alteration of pig back, which is an alteration of pickback, which is an alteration of pickpack, which is - no, that's where it stops!  In fact, etymologists aren't sure whether the original form was pickback or pickpack (though the earliest surviving form is picbacke from 1565).  The important word is actually pick, which, in this case, is thought to be a variant of the verb pitch or "to throw".  The back element would refer to one's back (spinal area), while the pack element would be "bundle of items for carrying".  The notion here is one of "throwing" something over one's back, or "throwing" a pack on one's shoulder.  Isn't it funny how we have a tendency turn an unfamiliar word into something more familiar in a relatively few generations?