Relatively position an element without it taking up space in document flow

Add a margin equal to the pixels that you moved:

Example

.box {
    position: relative;
    top: -30px; 
    margin-bottom: -30px;
}

You simply take that element off the document flow by setting position: absolute, and leave it's breaking point move freely with the dynamic flow of content by not specifying the left top right and bottom style properties which will be forcing it to use the relative endpoint of the flow dynamically. This way the absolutely positioned element will follow the document flow while removing itself from taking up the space.

No dummy wrappers are needed.

From reading up a little, it seems you can absolute position an element as long as the parent element is relatively positioned. That means if you have the CSS:

.parent { 
    position: relative; 
}
.parent > .child {
    position: absolute;
}

Then the child element won't take up any space in the document flow at all. You can then position it using one of the "left", "bottom", etc, properties. The relative positioning on the parent shouldn't usually affect it because it will be positioned at its original position by default if you don't specify "left", "bottom", etc.

http://css-tricks.com/absolute-positioning-inside-relative-positioning/

What you're trying to do sounds like absolute positioning. On the other hand, you can, however, make a pseudo-relative element, by creating a zero-width, zero-height, relatively positioned element, essentially solely for the purpose of creating a reference point for position, and an absolutely positioned element within that:

<div style="position: relative; width: 0; height: 0">
    <div style="position: absolute; left: 100px; top: 100px">
        Hi there, I'm 100px offset from where I ought to be, from the top and left.
    </div>
</div>