You have the Virtual Domains already created?
I've never tried, but I don't believe a list will respond to any domain other than the one you select when you create the list.
What would happen if you create a new list for the 2nd domain, then schedule a script to copy the subscription files from list1 to list2 on a regular basis.
This would give you 2 separate lists of the same name, and presumably would keep your subscription lists identical.
Something to think about, anyway.