In cases where we have done this, we just set the default value in the top list to what was selected. This way it comes up as selected, but the order of the drop-down doesn't change. Changing the order of the drop-down can be confusing for users, so you might want to consider this approach.

I believe using the attribute 'selected' like so:

<option value='stuff' selected>
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next to the one you want to select will do the trick. Note that the XHTML version of this is selected=selected.