Mapping C# long to ItemsChoiceType

Summary

Mapping C# long to ItemsChoiceType

Content

Hi,
  I am using RNT Version 17.8.0.1 which only has 6 choices for me (Yes/No, Date, DateTime, Integer, Text, Menu) when adding a new field in the custom object designer. In my Custom Object I want to create UserID which is long type in C# (bigint from Database). If I select ItemsChoiceType.Integer when I write my C# SOAP code I have to use something like

List<GenericField> gfs = new List<GenericField>(); 
gfs.Add(createGenericField("UserID", ItemsChoiceType.IntegerValue, (int) UserID));

But that will truncated UserID. I see there is 

ItemsChoiceType.LongValue

How can I define it in RNT agent Desktop Object Designer?