How to align last 3 menu items to the right

I would like create a menu with the first 3 items aligned to the left and last 3 items aligned to the right.

MENU:

<UL> 
<li>1a</li><li>2a</li><li>3a</li> <-left    right-> <li>4a</li><li>5a</li><li>6a</li>
</UL>

Using float left and right causes the last 3 items to change order, I need them to stay in order.

I would like a solution that does not require creating a separate menu or changing the order of the menu items to make the float:right put them back in the right order.