[ObrienDave]

Yes it can be done.
It would be a PITA to add a +.750 value to every instance of a Z value output.
I have never tried to do what you want, but, if you attach a copy of your post file I would be happy to give it a try.
I think it would be easier to move your model so the BOTTOM is Z+.750
That way you would not need the prompts, unless, of course, your stock thickness varies substantially.

P.S. PITA = Pain In The A**