CSS Regions could be a great help here but as of today they are work in progress and have very little browser support.
But what you could use is column-count
and column-gap
Here is a fiddle I whipped up: http://jsfiddle.net/MadLittleMods/wpTX7/
Here is some css to split it into columns horizontally within the 200px height.
#overflow_horizontal
{
height: 200px;
overflow: scroll;
-moz-column-count: 2;
-moz-column-gap: 24px;
-webkit-column-count: 2;
-webkit-column-gap: 24px;
column-count: 2;
column-gap: 24px;
}
Edit:
Here is a fallback. jsFiddle: http://jsfiddle.net/MadLittleMods/SEDaQ/
The fiddle does work but not on IE9 because it doesn't like text/plain resources. If you can get me a static link for Columnizer I can update the fiddle and it will work just fine.
Add Modernizr and Columnizer.
Add this jQuery(change # columns to whatever you need):
$('.no-csscolumns > #overflow_horizontal').columnize({
columns: 3
});