Actual dimension of an item in Keynote on presenter screen

Composing a Keynote Presentation for a client who would like to show an item that is .15 in thick(or 3.81mm) on the presenter screen. He wants it to appear on the screen as the actual size and not shown any bigger than it really is when projected onto the screen Can't think of any other way than moving the projector up to the screen until the thickness of the item is directly proportional to the size of the item on the screen. I know this sounds kind of whacky but does anyone else know of another method?