How to make one list split in half on the page

Question

I have a long list, similar to this, with 3 levels of indentation. However, it being very long I would like to break it at lets say 6.4 and make the list 50% width with half the list floating left and the other half floating right. A bit like this picture but with 2 instead of 3 columns.

http://alistapart.com/d/multicolumnlists/example0.gif

<ol class="main">
<li>MAIN HEADING
    <ol>
        <li>This is an example of a sub-clause and you can see that even though the words continue on to the right, it would be best if it wrapped around and formed a block to the right of the decimal number</li>
        <li>In doing so the normal second clause should also wrap around but the second subsequent clause should hang in from the left and be in a block.  See below for the remaining clauses
            <ol>
                <li>this list is completely for demonstration and should  not be construed as legal language in any way, nor should make sense in that</li>
                <li>should the indentation take  more than:
                    <ol>
                        <li>this many lines it would be overly big</li>
                        <li>legal numbering continues in the sub-sub clauses with the use of lower roman lettering and should flow below in a block</li>
                        <li>and continue the formatting on to the next line but be underneath the body of the the text and not begin directly below the number itself. In this example the text carries out to the right but I need it to wrap around underneath.</li>
                    </ol>
                </li>
            </ol>
        </li>
    </ol>
</li>
<li>Second Clause Heading
    <ol>
        <li>This is an example of a sub-clause and you can see that even though the words continue on to the right, it would be best if it wrapped around and formed a block to the right of the decimal number</li>
        <li>In doing so the normal second clause should also wrap around but the second subsequent clause should hang in from the left and be in a block.  See below for the remaining clauses</li>
    </ol>
</li>

I have tried to set the 'start="6"' but it doesn't allow for decimal places. Also, I am using a counter and adding the numbers through the css property 'content:'

Is there an easier way to do this?