In ServiceStack, how can I do integration testing with multiple endpoints?

We're using ServiceStack for a client project with several distinct problem domains, which we'd prefer to keep separated. We've developed a testing framework that spins up an AppHostHttpListener and sets up an in-memory test database using SQLite and DbUp - but, as you know, a test session's AppDomain can only have one AppHost at a time.

On the other hand, we have two different AppHosts that we want to deploy, let's call them Foo and Bar. Foo accepts requests and passes them to Bar, so Foo -> Bar, and Bar is standalone.

We want to be able to write end-to-end integration tests that exercise instances of both Foo and Bar. With ServiceStack's limitation of one AppHost per AppDomain, we seem to have the following options:

1. Spin up a new AppDomain for each AppHost inside the test session and control their lifetime across a MarshallByRef boundary. Not sure how this would perform sharing 'test connections' between AppHosts though.
2. Mock out the external service. This is the textbook answer, but these systems are critical enough that we'd like to see when changes to one service break the other.
3. Make the endpoints pluggable so that they can be loaded in the same AppHost for testing, but under different sub-URLs. The way I see it, this would require the endpoints to share AuthFeature, IDbConnectionFactory etc, so we would lose that flexibility.

My questions to you are:

1. Which option would you go with?
2. Can you recommend another approach that would enable us to test integration of multiple ServiceStack endpoints in memory?