Fixing widget to bottom of dynamic sidebars

Folks, I could use some advice. I have 3 column blog, central col is the posted content with a right and left sidebar. I'd like to have a text widget stuck to the bottom of one my sidebars. The problem is there is a gap between where my last widget ends and the position at the bottom for where I'd like a text widget to live. I don't know how to stick that text widget to the bottom, or shove some dynamic spacer between widgets. I figure the best method is to know the height of the central column since it's the tallest, but I don't know how to determine the size of the middle column to tell me what the bottom margin should be for my text widget.

So my question:
Is the best way to fix a widget to the bottom of a dynamic sidebar (meaning the sidebar gets longer as the central col gets resized with posts) is by having CSS inserts like "position: absolute, bottom: -some%" and the bottom margin should be the height of the central column?

E.g. text-widget

div#text-000123456 h1 {
font-size:1.0em;
font-weight: bold;
position: absolute;
bottom: -100%; //where this should be the height of the central col
}

Thanks.