Part Builder Question

[MarkPendergraft]

I am trying to create a part that derives the automatic surface elevation from the center of the rim of the structure, rather than the center of the structure itset.  In most situations, the difference would be minimal, but not all.  For example, when a Type II Catch Basin is situated underneath the curb and spun so the grate is in the road (picture attached).  In this situation the center is a half foot higher than the rim.

I've been through the part builder tutorial and can't seem to figure out if there is a way to seperate the autolayout point and the insertion rim elevation point.  Does anyone have any experience, knowledge, or advice on this?

Thanks for the help.

-Mark