There's also a product called One Finger Snap, which is
supposed to display the contextual menu when you click your single button and hold for a period of time (adjustable from 1/2 second to 3 seconds).
This is shareware with a license cost of only $6.85, but
test the free trial version first, because this tool seems
very quirky about where it will work. For example, it does not seem to work for copying URLs from browser windows (in Safari, it does nothing; in Firefox, it de-selects the URL before presenting the menu, so it can't be copied), nor does it copy text in MS
Word (where the Copy option is simply grayed out).
On the other hand, this is very new, and they seem pretty active about fixing bugs (going from release 1.0 to 1.2.2 in less than month), so maybe in time...
http://www.oldjewelsoftware.com/products/onefingersnap/index.html