@Michael - Actually I think the inset can do what I need it to do. You are probably already doing all the math needed under the hood for what i need- its just being used toward a different goal in the inset commands.
Set the thickness to 0 and then carve the edge out with a groove.
The groove is usually in the Hard plastic so boolean it out from the soft inset in blue and add it to the hard plastic in grey.
Thanks for sharing your thoughts guys! Very helpful. I think I have the start of something repeatable.