Hi Donald sorry for the delay in the answer.
In jBPM5 you have the concept of WorkItem that allows you to add your custom nodes with domain specific functionality.
Indise BPMN2 the concept of Service Task is used to model your processes and then in runtime you can bind a named Service Task (a Service task with a specific type) to a work item.
For creating a new work item with your specific functionality you need to create a new WorkItemHandler. For doing this you need to implement the WorkItemHandler interface. Please check the official documentation, in the Domain Specific Activities where the concept of work item handler is explained.
Cheers