I am not using Ubuntu, and I found an answer that also works on Centos here.
xmodmap -e 'pointer = 1 25 3 4 5 6 7 8 9'
If you have more mouse buttons, you keep adding them, this allows the pointer to be mapped to a different action, but middle mouse is kind of a pain now that we aren't using ancient mice with springs that require a kilogram of force.
