Enhancement: Modify opacity of a service within a theme

It would be great if the Opacity="<x>" tag could be added for services in themes. My scenario is that I have a hillshade service which I'd love combine in a theme with my high resolution imagery cache services with their opacity set to 40% as my users will never figure that out on their own, but I don't want to set the default opacity on those image services to that percentage in my site.