Use domain alias for template root uri

Hi

So I'm not sure if this is doable, and if it's even a problem for Mercator to solve but this seems like the best place to start. I'm using the plugin to allow me to have deploy specific domains to access a site by when we are doing phased deployment or just need to configure some settings before we switch the DNS over to the newly deployed install. Mercator works great for getting those deploy specific domains to load the site but the problem is all our asset urls load via the main site url which causes problems for testing and previewing the new code once deployed.

Is there a way for Mercator to override the setting for that, or is there something I'm missing that I can do do independently?

Thanks