... on the same machine - is it possible?

The reason I ask is that my company have an existing layered product which has two of it's physical layers deployed as web services running on IIS. We want to move to a SaaS (Software-as-a-service) model where our kit will host the services for multiple customers, and each will have a production and test instance.

So we might want to deploy 4 variants of the same web services, eg.
BusinessLayer.Customer1.Test
BusinessLayer.Customer1.Prod
BusinessLayer.Customer2.Test
BusinessLayer.Customer2.Prod

While our installation msi can create any of these web service names as it stands, installing any one replaces the previous version in IIS (and add/remove programs), even with Remove Previous Versions set to false. The reason I imagine is that the Product Code remains unchanged, and we don't really want to have to create one setup project per target build.

Does anyone have any advice on how to help achieve our objective?