I don't own a Surface Pro but I have an EP121 and have been involved in the design of toolbars for art programs using AHK. That has involved a lot of playing around trying to remap Wacom pen buttons and has been successful on pretty much any Wacom-based tablet PC. I've found that the best way is to just do a simple remap. Has wacom come up yet with a driver that allows you to assign different functions to the pen buttons (that's possible in Win 7 but I don't think it's yet available in Win 8, which I'm assuming your SP has)?
If not, is your pen button set to right-click? If that's the case, you can maybe just do a simple remapping like
If your pen button is indeed set to right-click, then you could also explore the use of something like "Keywait" or "GetKeyState" to "do something" as long as the pen button is pressed.
Remapping the eraser on Wacom pen seems to be pretty difficult as I've found that it's usually not detected by AHK or when looking at HID devices. Maybe there is a better way around, but the only way that I have found to remap the eraser is to modify the Wacom pen settings manually (and that is probably only available with a correct Wacom driver, which you may not have). If you are interested, you can find a description of what I've found here:
Note that in this Tablet PC forum, there are a lot of Autohotkey based solutions to make your use of your tablet easier. I would suggest you explore the following: