// This is the new lookup
private Common lookupWorker(FormReferenceControl _ctrl)
{
    SysReferenceTableLookup  tableLookup = SysReferenceTableLookup::newParameters(tableNum(HcmWorker), _ctrl);
    Query query = new Query();
    QueryBuildDataSource qbds = query.addDataSource(tableNum(HcmWorker));
    
    // Here you would have some ranges    

    tableLookup.parmQuery(query);
    tableLookup.addLookupfield(fieldNum(HcmWorker, Person));

    return tableLookup.performFormLookup();
}

// This is how you override the standard lookup
Dialog dialog = new Dialog("Select user");
DialogField df = dialog.addField(extendedTypeStr(HcmWorkerRecId),"User");

df.registerOverrideMethod(methodstr(FormReferenceControl, lookupReference),
                          methodstr(YourClass, lookupWorker),
                          this);

dialog.run();