Dynamically assign search help-functionality to a field

You can dynamically assign a Search Help name to a field. Here is the code you need.
 

IF rad1 EQ 'X' .                          " Sales Order
    matchcode_object = 'VMVA' .
  ELSEIF rad2 EQ 'X' .                      " Delivery
    matchcode_object = 'VMVL' .
  ELSEIF rad3 EQ 'X' OR rad4 EQ 'X' .       " Invoice
    matchcode_object = 'VMCF' .
  ENDIF .

  CALL FUNCTION 'HELP_VALUES_GET_WITH_MATCHCODE'
    EXPORTING
*     DISPLAY                         = ' '
*     FIELDNAME                       = ' '
*     INPUT_VALUE                     = ' '
      matchcode_object                = matchcode_object
*     TABNAME                         = ' '
    IMPORTING
      select_value                    = docno
    EXCEPTIONS
      invalid_dictionary_field        = 1
      invalid_matchdcode_object       = 2
      no_selection                    = 3
      OTHERS                          = 4 .
  IF sy-subrc <> 0.
  ENDIF.