To be honest, I'm not sure if it's even possible, but I'd like to try to find a way to auto-populate variants when a blank is selected on the Add/Edit Product page. This would also necessitate a rework of the Blanks settings area to allow pre-determining which sizes/colors are available for which blanks. That part of the equation wouldn't be too hard, but it's a moot point if we can't find a more automated way to handle product variants.