Simon, a bit late.....

I stumbled across this some time ago. This should be working similar in a participant. The code below is client code, I highlighted the important part. You call it with a URI to the remote object. See https://jazz.net/forum/questions/81826/how-an-operation-participant-works?page=1&focusedAnswerId=81979#81979 on how to save a work item in a participant.

    private static class LinkURIOperation extends WorkItemOperation {

       
        private URI fURI;
        private IEndPointDescriptor fEndpointDescriptor;
       
        public LinkURIOperation( IEndPointDescriptor endpointDescriptor,URI uri) {
            super("Linking URL", IWorkItem.FULL_PROFILE);
            fURI = uri;
            fEndpointDescriptor=endpointDescriptor;
        }

        @Override
        protected void execute(WorkItemWorkingCopy workingCopy,
                IProgressMonitor monitor) throws TeamRepositoryException {
            IReference reference;
                reference = IReferenceFactory.INSTANCE.createReferenceFromURI(fURI);
                workingCopy.getReferences().add(fEndpointDescriptor,reference);
        }
    }


To call it

                    URI uri=new URI("https://clm.example.com:9448/qm/oslc_qm/contexts/_Lm2UIACBEeGZqMjM3RLKTw/resources/com.ibm.rqm.planning.VersionedTestCase/_dJzNgQCBEeGZqMjM3RLKTw");
                    IEndPointDescriptor endpoint = ILinkTypeRegistry.INSTANCE.getLinkType(WorkItemLinkTypes.TESTED_BY_TEST_CASE).getTargetEndPointDescriptor();
                    LinkURIOperation linkOp = new LinkURIOperation(endpoint,uri);
                    linkOp.run(workItem, monitor);

//                    IEndPointDescriptor endpoint1 = //ILinkTypeRegistry.INSTANCE.getLinkType(WorkItemLinkTypes.AFFECTS_EXECUTION_RESULT).getTargetEndPointDescriptor();
//                    IEndPointDescriptor endpoint3 = //ILinkTypeRegistry.INSTANCE.getLinkType(WorkItemLinkTypes.AFFECTED_BY_DEFECT).getTargetEndPointDescriptor();