As of Thesis 1.8.5 this is no longer necessary as widget menus are treated like page widgets.
There’s been a couple people asking how to get a wp vertical nav in their sidebar. This post covers how to get over the technical css issues, the prettyfication you can do on your own after the fact.
Step 1 – Setup your wp-nav
Step 2 – Add the nav to your sidebar using the Custom Menu widget
Step 2 – Style it so it works, code below.