You can't. The toolbar in Adobe Reader X is static, there is no Quick Tools area nor any API/script access to add buttons other than in the Tools Pane.
This is a shocker Adobe. For adding comments to Reader-enabled PDFs, Reader 9 is much more accessible, flexible and intuitive than Reader X. The inability to add favourite commenting tools to a toolbar is disadvantageous to disabled users and requires two touches+ where one would have been possible before. I don't see any advantage of removing the toolbars to the end user. What were you thinking of?