Question: As this configuration is not supported I was wondering what alternatives people have used.

I have a universal app which currently uses a 4 tab UITabBarController on both the iPhone and iPad.

As I'd now like to use the splitviewcontroller I am faced with a design decision.

I guess I could just go with a toolbar at the top and go from there but was hoping there were more interesting techniques.

Answer: 
We use the command-line technique described by Marc Gravell in our service applications, so be sure to try it.

Note that you will be able to easily debug your application running as a true service on Windows XP and 2003, where you can interactively log into Session 0 and attach your debugger to the running service application. ["Session 0 isolation"](http://www.microsoft.com/whdc/system/sysinternals/session0changes.mspx), introduced in Windows Vista, makes it difficult to interact with/debug service applications so we end up doing our first round of testing and debugging on XP.

Good luck.
You're kind of on the right track when you talk about building a "helper application." You can build all the real logic of your application into a class library (dll) project, and then write a windows service that just calls the library. 

Then you can write other applications, say a console app or unit tests which reference your class library. 

That way you can write any front end application you want, and it just interfaces to the class library. That's also how you do unit tests, which would let you test most of the functionality without even really running the application... but that's really a bigger topic. :)