Override Ultimate Branding for a few custom domains on network

Hi,

I have ultimate branding set up to provide login and a few other styles on my network. I'd like to use a different login page on a few custom domains I've mapped to the network. Is this possible?

In other words, example.com/subdomain should all use Ultimate Branding but customdomain.com, which is mapped onto example.com/customdomain, should have its own login page.

Thanks,
Nathan