Eclipse (and most other IDE's I know) doesn't handle having "multiple" context roots elegantly but here is what I do currently:
You can simply just set the context root to "/" via the jboss specific descriptors and deploy it - then the only feature that gets funky is that "Run As..." no longer opens up your browser correctly. To fix that got to preferences of your project and see the "Web Project Settings" and set this to "./" and the url should be resolved correctly. (You can try with just "/" too but I've noticed there being problems with that and the path not being handled properly)
If you use Maven you can have m2e/wtp maintain this by adding:
to maven <properties> section.
This contextRoot you can of course control via profiles too if need be and thus you can avoid having your custom ant script do it.
This of course makes it necessary to deploy each war to its own server.
...got any suggestions how we can do it differently ? What we would need is someway to tell AS7 when deploying that this
war has a different context root without changing the war, but I don't know of a way to do this ?