How about using IoC container? With some thought you can end up with something on the lines of:
Dependency.Resolve<IFoo>(); You would have to specify which implementation of IFoo to use at a startup, but this is a one off configuration which you can easily replace later. Lifetime of a resolved instance can be normally controlled by an IoC container.
Static singleton void method could be replaced with:
Dependency.Resolve<IFoo>().DoSomething();Static singleton getter method could be replaced with:
var result = Dependency.Resolve<IFoo>().GetFoo();Example is relevant to .NET, but I'm certain very similar can be achieved in other languages.
