For the record, I wound up having to use a mechanism that works like so:

.leftcolumn {
	width: 200px;
	max-width: 200px;
	overflow: hidden;
	position: absolute;
	left: 0px;
	margin-left: 0;
	margin-right: 20;
}
.rightcolumn {
	background-color: #ffffff;
	display: block;
	margin-left: 199px;
}

Which eliminates the rather annoying overflow in the left margin (visually it goes "under" the right column, instead of over), but results in the footer being dependent solely on the right column's length (the absolute positioning means that the left column has been entirely ripped from the page flow.