Basically you will want to get a couple thousand points before starting this.

You might want to get the Sniper Rifle Persistant Perk that awards 300 points each kill. All you have to do is kill a couple zombies from a far away distance with any sniper rifle until you see a green mist. This will get you a nice couple thousand points.

What you will need.
-Points to start with
-Time Grenades
-Galva Knuckles

1.) On any round get a crawler and get Leroy to hold it, by giving Leroy candy while near the crawler, so the crawler isn't annoying you.

2.) Head into the bank from the secret tunnel located in the Gun Smith.

3.) Withdraw all money in the bank if you have any, after you have all the points you can throw down your time grenade.

4.) Head behind the counter and punch the two keys near the ground with the Galva knuckles and give away all your points into the power up.

5.) After you get rid of your points activate the Time Grenade and you will be sent back in time.

6.) You will have the same amount of points before but there will be the money drop that will give the points back that you deposited so pick it up. You can bank your points if you don't feel safe and think the game will end next round.

7.) Head back to step one until your bank is maxed out.