Yes, you can disable output conversion programmatically by overriding /IWBEP/CL_MGW_ABS_MODEL->DEFINE like that (makes use of some new ABAP syntax):
METHOD define.
super->define( ).
* Disable all output conversion since it is buggy
DATA(lt_type) = CAST /iwbep/if_mgw_odata_re_model( model )->get_entity_types( ).
LOOP AT lt_type ASSIGNING FIELD-SYMBOL(<s_type>).
DATA(lo_type) = model->get_entity_type( <s_type>-external_name ).
LOOP AT <s_type>-properties ASSIGNING FIELD-SYMBOL(<s_property>).
DATA(lo_property) = lo_type->get_property( <s_property>-external_name ).
lo_property->disable_conversion( ).
ENDLOOP.
ENDLOOP.
ENDMETHOD.