@JMiz: Nope, that would break the principles of encapsulation! What you're looking for is .NET Interfaces. An interface is essentially a contract, saying that Car class must implement the Drive() method, but the interface itself doesn't actually declare the implementation (method body). The method implementation is the responsibility of the class definition.
Unfortunately, while you can implement .NET Interfaces in PowerShell classes, you cannot declare an interface in PowerShell syntax.
Microsoft MVP: PowerShell