Serving multiple Rails apps from single domain

Question

I have two Rails apps that I want to serve with Passenger from the same domain.

I would like requests to come in to one app, and if that app is not able to handle the request, for the request to be passed to the the second app.

I know that I can use Passenger's RailsBaseURI option to deploy multiple apps to different sub URIs, but this doesn't give the behaviour I'm after.

Is there a standard way to achieve this?

Thanks in advance, etc etc.