AutoCAD Inventor :: Creating Casting Part From Machined Part

I have a part that is designed to be made from a casting. In my workflow it makes more sense to create the as machined part first and then base the casting on the machined part usually by using save as and then deleting the machined features. I understand that you can easily go the opposite direction by creating the cast and then creating a derived part that you apply the machining features to.

I tried to derive the casting in this way hoping that you could just suppress of delete features without altering the associativity between the two files but it appears that the derived part doesn't "know" about the features on the original, it's just a solid.

It would seem that this workflow would be a no brainer since most of the time the casting depends on the finished part which depends on the design specifications, so am I missing something or is there really no way to do what I want to do without having to go the messy route of having to manually alter two separate parts every time I alter the design?