Thats a pretty good question. I've never tried to do it like that.
Maybe you could do it this way
Position it relative to the lowest position div on the page. i.e. position it relative to your #maintext selector. Not sure if this will mess with your other stuff in your css I can't visually see what your CSS says
I have done this with Footer type divs on pages where there was not a lot of content. So I position the footer class to appear lower in relation to my .nav class to keep uniformity among the pages.
Cool what did you do?