store.js

import {applyMiddleware, createStore, combineReducers} from 'redux';

import {createSyncMiddleware} from '...somewhere';

export default function initStore(socket) {
  let middelware = applyMiddleware(/* redux-logger, thunk etc.*/);
  
  if (/* check if this is the 'leader' */) {
    middleware = applyMiddleware(createSyncMiddleware(socket), /* other middlware*/);
  }
  
  return createStore(
    combineReducers({/* your reducers */}),
    middleware
    );
}