To limit a selection to a subset of objects, filter the list of selection candidates in the selection controller model:

public class FilteredSelectControllerModel extends TLspSelectControllerModel {
  private final ILcdFilter<TLspDomainObjectContext> fFilter;

  public FilteredSelectControllerModel(ILcdFilter<TLspDomainObjectContext> aFilter) {
    super();
    fFilter = aFilter;
  }

  @Override
  public List<TLspDomainObjectContext> selectionCandidates(ALspSelectInput aInput,
                                                           Set<TLspPaintRepresentation> aRepresentations,
                                                           boolean aMultiple,
                                                           ILspView aView) {
    List<TLspDomainObjectContext> originalCandidates = super.selectionCandidates(aInput, aRepresentations, aMultiple, aView);
    //Use the filter passed in the constructor to filter the selection candidates
    return originalCandidates.stream()
                             .filter(fFilter)
                             .collect(Collectors.toList());
  }
}

You must install the controller model on the TLspSelectController by passing it in the constructor, or by calling the setControllerModel method.