1. There are no rules.
2. He who was the most buddies will pretty much always win regardless of your skill level.
3. Never go to a gun fight with a knife, never go to a knife fight with empty hand.
4. Don't fight within the paradigm of your training, use every available "weapon" at your disposal.
5. Refer to rule #1...there are no rules.
6. Use common sense, don't fight if the odds are not in your favor, better to retreat and live for another day, then to stand there and take a beating.
7. Always assume that you are out skilled, out numbered, or out weaponed. Therefore, don't fight unless you have to.
8. Get more friends, police or help to even the odds.
This is much better than any randori you could practice in any martial art, it is cheap (as all advice is
...easy (except on you ego), and easily implemented by all!
I don't think empty hand training does much for you if you are out numbered, or out weaponed.
Other than that...i pretty much agree with Larry. Not sure what adding realistic randori would accomplish in aikido that would greatly enhance your ability to survive a multiple opponent situation to be quite honest. It is nice to practice in principle, but you are living in la la land if you really think you can beat multiple opponents. If you do...you got lucky for some reason!
There is no holy grail that will prepare you to win or survive a multiple opponent situation as far as empty hand is concerned.