Wacom Maya Middle mouse button/scroll

I am using a wacom tablet with maya however I am unable to assign a middle mouse button to any of the buttons on the pen. Do some wacom tablets not come with this option? and if not what wacom tablets offer this feature?
I am using model PTZ630 however I need to work out the MMB issue as I am alternating between mouse and wacom however it is a disruptive workflow and using the pen is a lot kinder to my hand.