If you would like to add additional fields to the Delivery Due List - Transaction VL04. These fields do not exist in the list of additional fields in the IMG. You will need to have a user exit written. This OSS notes will help you in creating the additional fields :- 198137 - VL10: Customer-specific enhancements / user exits 415716 - User exits in delivery processing

Define your incomplete procedures in OVA2.
There are 3 levels :-
  Groups 
      Procedures
           Fields -> 1.  here you define the Status Group to used
                          2.  you define whether a warning message should be issued
 
Assign incompletion procedures to partner functions in SM30 - V_TPAR_VUV
Assign incompletion forms to the delivery types in SM30 - V_TVLK_VUV
Assign Incompletion Forms to the Delivery Item Types in SM30 - V_TVLP_VUV
 
Define the Status Group in SM30 - V_TVUVS
You use this function to block a document for delivery, billing, or pricing etc.
In an incompletion procedure you group together the fields that are to be checked for 
completion. If you have not entered data in one of the fields in the document, the document 
is incomplete. Depending on the status group you can block certain subsequent activities for 
the document.
For every field in the procedure you also have to define whether a warning message should 
be issued during processing if no data is entered in this field.