The only way to do this is to edit your actionmaps.xml in the "<install path>/USER/Profile/<profile name>" folder.
As its an xml its against the terms of service, but is the only way to do it unless you want to use macros to map your mouse wheel to the default 'Increase/Decrease Speed' buttons.
If you want to bind them to your mouse wheel via the xml, bind the actions you want to distinct keys. Like left and right alt. Then close the game. Go into your actionmaps.xml and search for "lalt" and "ralt". They should be in a section like this:
<action name="action_you_want"><rebind device="keyboard" input="mwheel_up" index="1" defaultInput="mouse3"/></action>
Make sure that device is "keyboard", input is either "mwheel_up" or "mwheel_down" and index is "1".
Save your edits, then open the game and you should be set. If you manage to completely break your control config then deleting the actionmaps.xml will reset them to default.