Orochimaru used a technique that can summon dead people (1st and 2nd Hokage). It was a technique only to bring back people from the dead. Something that is sealed is not considered dead. But its possible that there is a technique to unseal something for awhile and then have it sealed back to wherever it used to be (like summon Kyubi for awhile, then it goes back into Naruto). But the whole point of sealing something into someone is to make sure that it can never come back (unless someone unseals it) or to make sure nobody can ever control it.