How to override mouse button order for only one device with EVdev?

[Wolf Wings]

I have a ThinkPad T61p w/ a Synaptics touchpad AND thumbmouse. I
generally ignore the thumbmouse entirely except for one thing: The
thumbmouse has three buttons assigned to it, which are just above the
touchpad, which has two buttons assigned to it.

I'd like to associate the left and right mouse buttons on the
thumbmouse as mousewheel actions, but not change any of the mouse
button assignments on the touchpad's two buttons, nor do I want
3rd-button-emulation enabled on the touchpad.

Previously without EVDev, I could just use ButtonMapping and
ZAxisMapping to do this, but I can't find any documentation on how to
apply those (or if they even exist) when using the EVDev interface. Is
this even possible through EVDev? If not, can I just disable EVDev for
one or two devices so I don't have to manually configure all the other
event-driven inputs like hotkeys and lid switches and what-not?