Unable to map mouse wheel under control settings

In vanilla morrowin you can map the mousewheel going up/down to functions, like changing different weapons or magic spells on the fly. OpenMW at current isnt able to map the mousewheel up/down and map it to a function of your choosing under controls.

(RM-2679 from redmine: created on 2015-06-13 by William Sogge, , duplicates #4042 (closed))