Running multiple zope instances on a Windows server

We are running multiple zope instances on a Windows server. At present we can only run the initial instance as a Windows service. This was installed as a full Plone install. The other two instances were created using buildout.cfg and are run through the console using a scheduled task. This is not a robust solution and is affecting performance of the sites. Any ideas how we can install multiple Zope instances as Windows services.

I just wanted to add that this is the matching stackoverflow question: