Here are the responses that I received, I haven't had a chance to return to this project yet, but I'll post a summary of the responses since there was interest from others. What I was after was a parameter setting to allow this, but that doesn't exist. So the other solutions are listed below. Thanks for all the responses and your time.
Brian Parrish Thumb Tool & Eng. Bad Axe, MI
When I use a volume sequence and use a window that was created at the retract plane level of even Z0 (assuming Z0 is the top of the work piece) then I get a slice at Z0.
1.) Mod your mill vol (add protrusion to the top) by the amount of your depth of cut. 2.) Initially set zero above your part by your first depth of cut.
I haven't tried this myself, but I think that so long as you are using a mill volume, and not a window, there is a setting for "top surface" under sequence setup. This will allow you to specify where you want the cutting to start from.