You can acces the bookmarks in the Safari "Bookmark Bar" using the command key and a number represnting the order of the desired bookmark in the bar (see this hint). The neat thing is the bookmarks can be a line of JavaScript instead of an URL. Create a toolbar bookmark with the Google Scout code in it:
javascript:void(location.href='http://www.google.com/search?Enter as one line without any spaces! Shown on two lines for narrower display...
client=googlet&q=related:'+location.href)
Mac OS X Hints
http://hints.macworld.com/article.php?story=20030214073802535