Based upon this Nabble thread, it looks like you need to add a path route and then chain that path route to your hostname routes.
So perhaps something like:
; abstract routes to be used in chaining
resources.router.routes.plain.type = "Zend_Controller_Router_Route"
resources.router.routes.plain.abstract = true
resources.router.routes.plain.route = "/:controller/:action"
resources.router.routes.plain.defaults.controller = "index"
resources.router.routes.plain.defaults.action = "index"
resources.router.routes.mysite.type = "Zend_Controller_Router_Route_Hostname"
resources.router.routes.mysite.abstract = true
resources.router.routes.mysite.route = "www.mysite.com"
resources.router.routes.mysite.defaults.module = "mysite"
resources.router.routes.mysite1.type = "Zend_Controller_Router_Route_Hostname"
resources.router.routes.mysite1.abstract = true
resources.router.routes.mysite1.route = "www.mysite1.com"
resources.router.routes.mysite1.defaults.module = "mysite1"
; now the actual (non-abstract) routes are chains of the abstract ones
resources.router.routes.mysite-plain.type = "Zend_Controller_Router_Route_Chain"
resources.router.routes.mysite-plain.chain = "mysite,plain"
resources.router.routes.mysite1-plain.type = "Zend_Controller_Router_Route_Chain"
resources.router.routes.mysite1-plain.chain = "mysite1,plain"
Actually, we could probably collapse the two abstract mysiteX routes into a single abstract route using a placeholder like :site
to stand in for the mysiteX
value and set some requirements/defaults on those, but I think this conveys the idea.
Not tested - actually I have never played with chained routes before - but it seems that something like this is required to make the hostname routing work.