If you don't mind a bit of Javascript, you can do without changing the HTML structure at all. It works by setting position: fixed; top: auto; left: auto; position: fixed; top: auto; left: auto; on thing , and then adjusting the position of the thing when scrolling the page - I do this through the css margin-top css property.
Example: http://jsfiddle.net/sparebytes/zxwL8/
One problem is that each ancestor of a thing must have a scroll event associated with it, since this event does not create a bubble chain.
Edit Rollback is something that can be disabled if it passes by the bottom of the body , because fixed elements cannot make their parents bigger
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