By placing a jar on the project's classpath, the designer should be able to allow the user to define properties of a custom service task as specified in the jar. This entails offering an interface / abstract base class to implement / extend in the jar and specifying a manifest declaration to look for in the jar. Simple properties should be supported and the jar developer can also indicate if and how to include the service task in a separate palette drawer. Obviously, this should result in an instantiation and invocation of the overriding class as part of the service task.
Exact feature set and implementation in the designer tbd.