You need to create a custom endcap for it that basically made of a polyline with width. I haven't used ADT3.3 for awile, so I don't remember the exact procedure. (2004 is easier!) When you apply the endcap, it will appear blank. When creating encaps, if the pline has a width, it won't show, if it has no width then it will.
Look in the help for endcaps, and see if that helps you at all.
Chris