Modify physical dimension based on quantity selection when adding to cart

I would like to create a product that is sold by length. For example, a .25" diameter threaded rod that can be custom cut to a desired length in inches (up to 72")
So, if the product dimensions are:
length .25"
width: .25"
height: (Variable, based on the length/quantity selected by the customer when adding the product to the cart.)

Is there a way, using rules or otherwise, to multiply a physical dimension by a factor? This may be a feature request for rules integration, but I'm requesting support for this particular use case if there's already an answer or others are facing a similar challenge.