This isn't something that Ractive currently supports, though it might in future. You could try doing the following:
frag = document.createDocumentFragment();
// move contents into the document fragment...
while ( oRactive.el.firstChild ) {
frag.appendChild( oRactive.el.firstChild );
}
// ...then into the DOM
someOtherDomElement.appendChild( frag );
// update oRactive.el so oRactive.find() still works
oRactive.el = someOtherDomElement;
Ractive stores references to individual nodes - in most cases it doesn't care about the actual shape of the DOM, and your situation shouldn't pose any obstacles (though I'd be interested to know if you run into any bugs doing this).